Given the function f(x) = 6(x+2) − 3, solve for the inverse function when x = 21.

F(x) = 6(x +2)  - 3

let y = f(x)

y = 6x + 12 - 3
 
 y = 6x + 9   solving for x.

y - 9 = 6x

6x = y - 9

x = (y - 9)/6

Recall   f(x) = y.   Implies  x = f⁻¹(y)

x = (y - 9)/6

f⁻¹(y) = (y - 9)/6

So as well:

f⁻¹(x) = (x - 9)/6          when x = 21

f⁻¹(21) = (21 - 9)/6 = 12/6 = 2

f⁻¹(21) = 2

You are dumb you will drop out of high school