Hi Ellen,

You didn't give instructions but I assume you are to "simplify" or "write without the negative exponent". You have

\[\frac{7}{a b^{-4}}.\]

First of all focus on the denominator alone to get

\[a b^{-4} = a \times \frac{1}{b^4} = \frac{a}{b^4}.\]

The original expression then can be written as

\[\frac{7}{\frac{a}{b^4}} = 7 \times \frac{b^4}{a} = \frac{7 b^4}{a}\]

I hope this helps,

Penny