The fully factored form of the quadratic is (2r - 7)(r + 6).
2r^2 + 5r - 42
Check if splitting the middle term is possible.
List factors of -84
1 * -84
-1 * 84
2 * -42
-2 * 42
3 * -28
-3 * 28
4 * -21
-4 * 21
6 * -14
-6 * 14
7 * -12
-7 * 12 (these digits satisfy the criteria.)
Split the middle term.
2r^2 + 12r - 7r - 42
Factor by grouping.
2r(r + 6) - 7(r + 6)
Rearrange.
(2r - 7)(r + 6)