Hey there!
Our function is:
f(x) = 4^x
If we want to have f(3), we simply can plug in 3 to our answer, and evalutate from there:
f(x) = 4^3 =
4*4*4 =
16*4 =
64
We just calculated 4 to the fourth power, which is four times four times four times four. Therefore, 4 of four is equal to 64.
Hope this helps!