$$\text { Find the formula for } d f ^ { - 1 } / d x \text {. }$$

Multiple Choice

$$\text { Find the formula for } d f ^ { - 1 } / d x \text {. }$$
- $$f ( x ) = 243 x ^ { 5 }$$

A) $\frac { x ^ { 1 / 5 } } { 3 }$
B) $\frac { 1 } { 15 x ^ { 4 / 5 } }$
C) $1215 x ^ { 4 }$
D) $15 x ^ { 4 }$