assuming you mean[tex] \frac{7ab^{-2}}{3w} [/tex]
reember
(ab)/c=(a/c)b
also
[tex]x^{-m}= \frac{1}{x^m} [/tex]
so
[tex] \frac{7ab^{-2}}{3w} [/tex]=
[tex]( \frac{7a}{3w})(b^{-2}) [/tex]=
[tex]( \frac{7a}{3w})(\frac{1}{b^2}) [/tex]=
[tex] \frac{7a}{3wb^2} [/tex]
