Evaluating a function in a specific point means to substitute all occurrences of x with the specific value.
In your case, we have to substitute "x" with "a+h":
[tex]f(x)= -5+4x^2 \implies f(a+h) = -5+4(a+h)^2\\ = -5+4(a^2+2ah+h^2)=-5+4a^2+8ah+h^2[/tex]
