Assigment of conditional statement

From where Can I get the answer of assignment ?
your answer really help me for improvement.
I am not able to understand whether I write proper code or not ? or at which point I make mistake.

following is my code to calculate marks and percentage. can you help me by checking the my code… whether code is proper or not ?

Students Marks Student Marks
       </form>
   
    </table>       

<?php if (isset($_POST['submit'])){ $total_marks = $_POST['physics']+ $_POST['chemistry']+$_POST['biology']+$_POST['matematics']+ $_POST['computer']; echo "

"; echo "Total Marks is " . $total_marks."
" ; echo "Percentage is " . ($total_marks/5) ; echo "

"; } ?>
Physics
Chemistry
Biology
Matematics
Computer