g(x)=4x-3, find g(3a). Substitute "3a" for x. g(3a) = 4(3a) - 3 = 12a - 3 given f(x)=x^2 - x+7, find f(0) Substitue "0" for x. f(0) = 0^2 - 0 + 7 = 7