#### Answer

$3(r+t)^{2}$

#### Work Step by Step

The greatest common factor of a group of terms is the greatest factor that evenly divides into all terms in the group.
In this case, $3(r+t)^{2}$ is the greatest common factor, because it is the largest factor that divides evenly into both terms.
$6m(r+t)^{2}\div3(r+t)^{2}=2m$
$3p(r+t)^{4}\div3(r+t)^{2}=p(r+t)^{2}$