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