Given the function f (x) = 5 (x+4) - 6 solve for the inverse function when x=19

F (x) = 5 (x + 4) - 6

let y = f (x)

y = 5x + 20 - 6 solving for x.

y = 5x + 14

y - 14 = 5x

5x = y - 14

x = (y - 14) / 5

Recall f (x) = y. Implies x = f⁻¹ (y)

x = (y - 14) / 5

f⁻¹ (y) = (y - 14) / 5

So as well:

f⁻¹ (x) = (x - 14) / 5 when x = 19

f⁻¹ (19) = (19 - 14) / 5 = 5/5

f⁻¹ (19) = 1