f(x) = 5 ( x + 4) - 6
y = 5 (x + 4)
interchange x and y and then solve for y
x = 5 (y + 4)
[tex] \frac{x}{5} = y + 4 [/tex]
[tex] y = \frac{x}{5} - 4[/tex]
∴ [tex]f ^{-1} (x) = \frac{x}{5} - 4
[/tex]
Solve for x= 19 for the inverse found
[tex]f ^{-1} (19) = \frac{19}{5} - 4 [/tex]
[tex]f ^{-1} (19) = - \frac{1}{5}[/tex]
