Step 1 :Given function: \(f(x) = -3x - 6\)
Step 2 :Replace \(f(x)\) with y: \(y = -3x - 6\)
Step 3 :Swap x and y: \(x = -3y - 6\)
Step 4 :Solve for y: \(y = \frac{x+6}{-3}\)
Step 5 :\(\boxed{f^{-1}(x) = \frac{x+6}{-3}}\)