7 класс 2 примера помогите прошу

1) [latex] \frac{b-3}{8 b^{4} } * \frac{3b}{ b^{2} -9} = \frac{(b-3)*3b}{8 b^{4}(b-3)(b+3) } = \frac{3}{8 b^{3}(b+3) }= \\ =\frac{3}{8 b^{4}+24 b^{3} }[/latex] 2) [latex] \frac{4-b}{ b^{2}-6b+9 } * \frac{3b-9}{ b^{2}-16 } = \frac{-(b-4)*3(b-3)}{(b-3)^{2} *(b-4)(b+4)} = \\ \frac{-3}{(b-3)(b+4)} =\frac{3}{(3-b)(b+4)} = \frac{3}{- b^{2}-b+12 } [/latex]