How to perform Mathematical operations in Mysql through php and Mysql?

I am new to Mysql and have faced this problem while learning:- I Created a table named "x" with 10 columns and wrote a code in PHP to enter the data into a table from a form in first 8 columns of table and in column 9 I need to a value that will be obtained after the performing mathematical operation on the value in column 2. For instance, I have marks for every student in column 2 of the table and in column 9, I need their percentage (considering total marks are constant). How can I get the percentage in column 9 and update that on every row of column 9?