Solution: We have to multiply the term outside the bracket, $pqr$, by each term inside the bracket. Make sure you’re familiar with the laws of indices before trying to tackle this question.
\begin{aligned}pqr(5pr +5r^5 -25pqr)&=pqr\times 5pr + pqr\times 5r^5 - pqr\times 25pqr \\ &=5p^{2}qr^{2} + 5pqr^6 - 25p^{2}q^{2}r^{2} \end{aligned}