Answer
$3(m-2n-5)$
Work Step by Step
Find a common factor for each term. That factor can be used as the term that was "distributed across" the difference.
3 is a common factor. Recreate the difference be dividing each term by 3.
$3m\div3=m$
$6n\div3=2n$
$15\div3=5$
$3m-6n-15=3(m-2n-5)$
