(f○g)(x) = f(g(x)) = 6g(x)-9 = 6(8x+10)-9 = 48x+60-9 = 48x+51
(g○f)(x) = g(f(x)) = 8f(x)+10 = 8(6x-9)+10 = 48x-72+10 = 48x-62