<?php 
                                //variable for student 
                                $student1 =["name" => "manoj", "mark" => 90, 'total_fee' => 5000, 'paid'=>1000, 'income'=>10000];                                
                                $marks = $student1['marks'];
                                if ($marks>=60)
                                {
                                      $grade = "First Division";
                                }
                                else if($marks>=45)
                                {
                                      $grade = "Second Division";
                                }
                                else if($marks>=33)
                                {
                                      $grade = "Third Division";
                                }
                                else
                                {
                                      $grade = "Fail";
                                }                                
                                $pending_fee=$student1['total_fee']-$student1['paid'];
                                if($student1['income']>2000){
                                    echo 'Not eligible for scholarship';
                                }
                                else{
                                    echo 'Eligible for scholarship';
                                }                             
                                $teacher1 =["name" => "manoj", "age" => 45, 'basic' => 5000, 'ta'=>1000, 'hra'=>10000];
                                $total_salary= $teacher1['basic']+$teacher1['ta']+$teacher1['hra'];
                                if( $teacher1['age']>55){
                                   echo 'Retirement Age';
                                }
                                $bus1 =["no" => "kL0723", "model" => 2000, 'insurance' => '2023-08-10']; 
                                $next_test=2023-$bus1['model'];
                                if($next_test>15){
                                    echo 'Need re-test';
                                }
                                


                                ?>

                   

Note that the above code, we have implemented logic of three tasks, 1) find grade, 2) find pending fee , 3) find scholoarship eligibility
In this approach , the code maintance , modification and dubugging are not easy. Define separate functions based on each logic for making the code easier to maintain, modify and debug

                       <?php 
                        function findGrade($marks){

                                if ($marks>=60)
                                {
                                      $grade = "First Division";
                                }
                                else if($marks>=45)
                                {
                                      $grade = "Second Division";
                                }
                                else if($marks>=33)
                                {
                                      $grade = "Third Division";
                                }
                                else
                                {
                                      $grade = "Fail";
                                }

                                return $grade;

                        } 
                        function findFee($total_fee, $paid ){
                            $pending_fee=$total_fee-$paid;
                        }
                        function findScholarship($income ){
                               if($income>2000){
                                    echo 'Not eligible for scholarship';
                                }
                                else{
                                    echo 'Eligible for scholarship';
                                }
                        }

                        function findSalary(){

                        }

                        function findRetirement(){

                        }

                        function findRenewal(){
                              
                        }
                        



                      
                        ?>