Answer
The side length of the square is
$5r+3$.
Work Step by Step
$25r^{2}+30r+9=$
...write first and last terms as squares.
$=(5r)^{2}+30r+(3)^{2}$
...does middle term equal $2ab$?
$30r=2\cdot(5r)\cdot(3)$
$=(5r)^{2}+2\cdot(5r)\cdot(3)+(3)^{2}$
...write as the square of a binomial.
$=(5r+3)^{2}$
