Answer
$\color{blue}{(5s^2+3t)(5s^2-3t)}$
Work Step by Step
Note that $25s^4=(5s^2)^2$ and $9t^2=(3t)^2$.
Thus, the given binomial is equivalent to:
$=(5s^2)^2-(3t)^2$
Factor using the formula $a^2-b^2=(a+b)(a-b)$ where $a=5s^2$ and $b=3t$ to obtain:
$=\color{blue}{(5s^2+3t)(5s^2-3t)}$
