Answer
(s-15t)(s+5t)
Work Step by Step
You are given $s^{2}$-10st-75$t^{2}$. Factor it out:
$s^{2}$-15st+5st-75$t^{2}$ -break out the middle value-
($s^{2}$-15st)+(5st-75$t^{2}$) -group the first two and last two terms-
s(s-15t)+5t(s-15t) -Find the GCF of each grouping-
(s+5t)(s-15t) -factor out the common term-
=(s+5t)(s-15t)
