Question 919994
f(f(f(x))) = f(f(px+q)) = f(p(px+q) + q) = p(p(px+q) + q) + q = 8x + 21


We see that the x coefficient is p^3 = 8, so p = 2. If we let x = 0, for example, we have


2(2(2*0 + q) + q) + q = 21
2(2(q) + q) + q = 21
7q = 21
q = 3