Given the functions, f(x) = 3x - 6 and g(x) = x2 + 5x + 7, perform the indicated operation. When applicable, state the domain restriction. f(g(x)) x2 + 8 x + 1 3 x3 - x2 - 9 x - 42 3 x2 + 15 x + 21 3 x2 + 15 x + 15