Fill in the blank with a constant, so that the resulting expression can be factored as the product of two linear factors.
3mn - 6m + 15n + ___
3mn-6m=3n
3n+15n=18n
3mn - 6m + 15n + -----
3m ( n - 2) + 15n - 30 =
3m ( n - 2) + 15 ( n - 2) =
(n - 2) ( 3m + 15)
