Answer
$(x-2y)(3x+5y)$
Work Step by Step
Using factoring by grouping, the given expression, $
3x^2-6xy+5xy-10y^2
,$ is equivalent to
\begin{array}{l}\require{cancel}
(3x^2-6xy)+(5xy-10y^2)
\\\\=
3x(x-2y)+5y(x-2y)
\\\\=
(x-2y)(3x+5y)
.\end{array}