How do i solve this f(x) = 3x for x = –5

F(x)= 3x

So, you're going to replace the X with -5 in parentheses which will indicate you are multiplying. 

The equation will look like this F(x)=3(-5)  AKA 3*-5    which equals -15
-15 is the answer. Hope this helped.

Are you trying to figure out the volume?