Answer
-$x^{4}$$y^{12}$
Work Step by Step
You have the expression ($x^{3}$$y^{5}$) $\times$ ($-y^{7}$x) and have to simplify it:
($x^{3}$$y^{5}$) $\times$ ($-y^{7}$x) =-($x^{3+1}$)($y^{5+7}$) -to multiply powers with the same base add the exponents-
=-$x^{4}$$y^{12}$
