I would like a very simple math app that could be placed on my website that a visitor could enter their data and get an instant result. 

ie

a +b+c divided by d multiplied by e = The answer. 

the user enters their known data for each specifically named category abcd, so the only unknown is the answer. 

4 + 7 + 9 /  8 x 6 = ?

( 15 ) would be seen as the result.