First note that f(x) means the same thing as y. To solve for f(x) or y you need to plug in -5 for x and solve using the rules of PEMDAS
5(-5) + 40
-25 + 40
15
When x is -5 then y is 15
Hope this helped!
~Just a girl in love with Shawn Mendes
Excuse me is that a statement or a question because you do not make it sound like one.