Answer :

[tex]3m^2n+12mn^2[/tex]
In both the sets, 3 and m as well as n can be found as common factors.
So,
3mn( m+4n)


Therefore the answer is 3mn (#3)
3m²n + 12mn²
3mn(m) + 3mn(4n)
3mn(m + 4n)

The GCF of 3m²n + 12mn² is 3mn.