Question 1209739
Here's how to find the constant:

1. **Combine Like Terms:**
   First, combine the like terms in the expression:

   2mn - 18m + 5n - mn + 20m + 4n + C = mn + 2m + 9n + C

2. **Factoring Pattern:**
   We want this expression to be factorable into the form (m + a)(n + b) for some constants *a* and *b*.  Expanding this factored form gives us:

   mn + bm + an + ab

3. **Match Coefficients:**
   Compare the coefficients of the terms in our simplified expression (mn + 2m + 9n + C) with the coefficients in the expanded factored form (mn + bm + an + ab):

   * The coefficient of mn is 1 in both.
   * The coefficient of m is 2, so b = 2.
   * The coefficient of n is 9, so a = 9.
   * The constant term is C, and it must equal ab.

4. **Solve for C:**
   Since a = 9 and b = 2, we have:

   C = ab = (9)(2) = 18

Therefore, the constant is 18. The factored expression is (m+9)(n+2).