Answer: [tex]\bold{\dfrac{1}{(bm)^3}}[/tex]
Step-by-step explanation:
To make the exponent positive, flip the fraction.
[tex](bm)^{-3}=\dfrac{1}{(bm)^3}\\\\\text{You can distribute the exponent to get: }\dfrac{1}{b^3m^3}[/tex]