Answer:
[tex]\left(m+7\right)\left(n-1\right)[/tex]
Step-by-step explanation:
[tex]mn+7n-m-7[/tex]
[tex]\left(mn+7n\right)+\left(-m-7\right)[/tex]
[tex]n\left(m+7\right)-1\left(m+7\right)[/tex]
