Sum columns from database using checkbox

I am new to php. I have inserted only a single value in two columns of database. I am trying to add them both using checkbox. Forexample. There is a column with name "englishprice" with only one value 20, and another column "mathprice" with only value 10. I want to sum them using checkbox, Like if i only check englishprice then it shows its price, if i check both then it sums both.