Select a sign ($+$ or $-$) and fill in the blank with a constant, so that the resulting expression can be factored as the product of two linear factors. 2mn - 21m + 5n - mn + 14m + 6n + ___
Simplify as
mn - 7m + 11n
m ( n - 7) + 11(n - 7) = (m + 11) ( n - 7)
mn - 7m + 11n - 77
+355 
