You are treating integer 15 as a function.
You need to use *, because if you strictly include parentheses ( ) after an integer, program assumes that you are calling the integer as a function.
(You'll learn about functions in 3rd module of the Python 3 tutorial.)
Just put * between 15 and (b-40) and your program should work fine.
Parto Ghahramani you are missing the asterisk symbol "*" for multiplication before the brackets in the print after else condition. Please look at the code