(5y)(2y3)

I assume we have

(5y)x(2y^3) =

10y^4

$$\left({\mathtt{5}}{\mathtt{\,\times\,}}{\mathtt{y}}\right){\mathtt{\,\times\,}}\left({\mathtt{2}}{\mathtt{\,\times\,}}{\mathtt{y3}}\right) = {\mathtt{30}}{\mathtt{\,\times\,}}{{\mathtt{y}}}^{{\mathtt{2}}}$$