Step-by-step solution:
1. Replace y with the function's output:
y = 6 \log_5 (3x^3 - 6)
2. Switch x and y to find the inverse:
x = 6 \log_5 (3y^3 - 6)
3. Isolate the logarithmic term by dividing both sides by 6:
\frac{x}{6} = \log_5 (3y^3 - 6)
4. Rewrite the logarithmic equation in exponential form:
5^{\frac{x}{6}} = 3y^3 - 6
5. Solve for y :
3y^3 = 5^{\frac{x}{6}} + 6
6. Divide by 3:
y^3 = \frac{5^{\frac{x}{6}} + 6}{3}
7. Take the cube root of both sides to solve for y :
y = \sqrt[3]{\frac{5^{\frac{x}{6}} + 6}{3}}
8. Replace y with f^{-1}(x) :
f^{-1}(x) = \sqrt[3]{\frac{5^{\frac{x}{6}} + 6}{3}}