Answer
$(5m+8)^{2}$
Work Step by Step
$25m^{2}+80m+64=$
...write first and last terms as squares.
$=(5m)^{2}+80m+(8)^{2}$
...does middle term equal $2ab$?
$80m=2\cdot(5m)\cdot(8)$
yes.
$=(5m)^{2}+2\cdot(5m)\cdot(8)+(8)^{2}$
...write as the square of a binomial.
$=(5m+8)^{2}$
