Answer
$7xy^2(-x^3+2y+3y^2$)
Work Step by Step
$Factor$ $out$ $the$ $common$ $factor:$
$-7x^4y^2+14xy^3+21xy^4$
All the terms have a common factor of $7xy^2$
$\frac{-7x^4y^2}{7xy^2} = -x^3$
$\frac{14xy^3}{7xy^2} = 2y$
$\frac{21xy^4}{7xy^2} = 3y^2$
$=7xy^2(-x^3+2y+3y^2$)