fx=2x+5 (fog^-1)(x)=-15+24x/4x-3 (g^-1)(x)?

f(x)= 2x+5
y = 2x+5
-2x = 5-y
x = (5-y) / -2
f(x)⁻¹ = ( 5-x) / -2

(fog)⁻¹ = -15+24x / 4x - 3
f ( g(x) )⁻¹ = -15 + 24x / 4x - 3
( 5 - g(x)⁻¹) = -15 + 24x
     -2             4x - 3
(4x - 3) ( 5- g(x)⁻¹ ) = 30 - 48x
20x -4x g(x)⁻¹ - 15 + 3 g(x)⁻¹ = 30 - 48 x
68 x - 45 = 4x g(x)⁻¹ - 3 g(x)⁻¹
68x - 45 = g(x)⁻¹ (4x - 3)
g(x)⁻¹ = 68x-45
            4x - 3