To solve this problem you must apply the proccedure shown below:
1. You have the following expression given in the problem above:
[tex] mn - 4m - 5n + 20 [/tex]
2. The first thing you must do to factor the expression is to group the terms, as following:
[tex] (mn-4m)+(-5n+20) [/tex]
3. Now, choose the greatest common factor of each group:
[tex] m(n-4)-5(n-4) [/tex]
4. Now, you need to factor the expression by factoring out the [tex] n-4 [/tex]
[tex] (m-5)(n-4) [/tex]
The answer is: [tex] (m-5)(n-4) [/tex]
