Answer:
[tex]\frac{4^{15} }{b^{21} }[/tex]
Step-by-step explanation:
You would multiply the powers, so 7*-3 which is -21 and 5*-3 which is -15 but since you cannot have a negative power in the numerator of a fraction you switch [tex]b^{-21}[/tex] and [tex]4^{-15}[/tex] which becomes [tex]\frac{4^{15} }{b^{21} }[/tex].
hope this helps:)
