I will be thrilled if anyone could help me out with this problem.

The problem is If f(x)=x+5
Find F (-5)

I got f(x) =(-5)+5

x=0

I keep second guessing myself.

Well, you're right.

except the x = 0 part.

if f(x) = x + 5

F(-5) = -5 + 5 = 0

so x doesn't equal 0

F(-5) = 0