(a) Start with f(x)= 3x − 5; y=3x - 5, and switch x and y before rearanging to get y in terms of x again:
y=3x - 5
x=3y - 5
(x+5)/3=y
Therefore f^−1(x)=(x+5)/3
(b) Start with f(x)= 3x − 5 and and sub result into g^−1(x) = x + 2:
(g^−1 o f)(x) = (3x − 5) + 2 = 3x - 3
(c) (f^−1 o g)(x) = (g^−1 o f)(x)
(x + 3)/3 = 3x - 3
x + 3 = 9x - 9
12 = 8x
3/2 = x