+900 Fill in the blank with a constant, so that the resulting expression can be factored as the product of two linear expressions:
2mn - 18m + 5n - mn + 20m + 4n + ___
+11 18, trust me since you must combine like terms, then plug in two variables to group terms, and finally multiply the value of the variables after you compare the two expressions that you get by first combining like terms, then grouping terms with variables.
