How to calculate inverse of any function?

Let f (x) = 2x + 5
Find the inverse.

Let y = f (x) = 2x + 5 and g (y) = x
g is the inverse function.

2x = y - 5
x = [ y - 5 ] / 2
g (y) = [ y - 5 ] / 2
g (x) = [ x - 5 ] / 2_______inverse function.