Question

If f(x)=4x^2+5x, what is f(a+4)

Answer 1

if f(x), then f(a+4) would mean that x=a+4. substitute this into the equation.
thus,
f(a+4) = 4(a+4)^2 + 5(a+4)
= 4(a+4)(a+4) + 5a + 20
= 4(a^2+8a+16) + 5a+20
= 4a^2+32a+64 +5a+20
f(a+4) =4a^2+37a+84
Answer is B.

Hope this helps :)