Let f(x) = 2x − 6. solve f−1(x) when x = 2.

To find the inverse of ƒ(x) = 2x - 6, then let ƒ(x) be y
y = 2x - 6
=> Make x the subject of formula by adding 6 to both sides and then dividing by 2, which you'll have
(y + 6)/2 = x
=> Switch the x & y variables to get the inverse of y, then
(x + 6)/2 = y
=> Remember that ƒ(x) is y, so also the inverse of y is ƒ-1(x), then
ƒ-1(x) = (x + 6)/2, where x = 2, you'll have
ƒ-1(2) = (2 + 6)/2
ƒ-1(2) = 8/2
ƒ-1(2) = 4