Factor the equation 3m^2n+12mn^2

hopefully this is right it should be

3mn • (m + 4n)

That's not an equation. It's just an expression that stands for a number.

Of course, we can't find the number until we know what 'm' and 'n' are.

The largest "common factor" is 3mn.

So in factored form, the expression is 3mn (m + 4n).