g(x) =5x+5 f(x)= 2x2-5x+1 (g o f) invers (3).......

g o f (x) = g [f(x)]
= g (2x²-5x+1)
= 5 (2x²-5x+1) + 5
= 10x² - 25 x +5

jadi (g o f) invers (3) = 10 (3)² - 25 (3) +5 = 90-75+5 =20