f(x) = 4x + 3
g(x) = -2x + 5
(f o g) (5) means the function of g when g is a function of 5
(the function of the function concept)
so we need to get g(5) firstly
g(x) = -2x + 5
g(5)= -2(5) + 5 = -5
After that, f(g(5)) = f(-5) = 4(-5) + 3 = -20 + 3 = -17
I hope that helps