How do you explain mental math to multiple two numbers

Which answer choice listed below is thewhich answer choice listed below is the inverse function of ƒ(x) = x-3 x+3 , x ≠ -3? a) ƒ-1(x) = 3 ( x+1 x-1 ), x ≠ 1 b) ƒ-1(x) = -3 ( x+1 x-1 ), x ≠ 1 c) ƒ-1(x) = 3 ( x-1 x+1 ), x ≠ -1 d) ƒ-1(x) = -3 ( x-1 x+1 ), x ≠ -1inverse function of ƒ(x) = x-3 x+3 , x ≠ -3?