Answer
(x-3y)(x+6y)
Work Step by Step
You are given $x^{2}$+3xy-18$y^{2}$. Factor it out:
$x^{2}$+6xy-3xy-18$y^{2}$ -break out the middle value-
($x^{2}$+6xy)+(-3xy-18$y^{2}$) -group the first two and last two terms-
x(x+6y)-3y(x+6y) -Find the GCF of each grouping-
(x-3y)(x+6y) -factor out the common term-
=(x-3y)(x+6y)
