F(x) = 3x + 1 and f^-1=x-1/3
then f(2)

Input:

{F(x) = 3 x + 1, 1/f = x - 1/3 f(2)}

Result:

{F(x) = 3 x + 1, 1/f = x - f(2)/3}

Alternate forms:

{3 x + 1 = F(x), 3 x = f(2) + 3/f}

{F(x) = 3 x + 1, f(2) = 3 x - 3/f}

{F(x) = 3 x + 1, 1/f = 1/3 (3 x - f(2))}

Alternate form assuming f and x are positive:

{3 x + 1 = F(x), 3 f x = f(2) f + 3}

-2 is the right