12w = 6 · 2w
18 = 6 · 3
12w - 18 = 6 · 2w - 6 · 3 = 6(2w - 3)
factor 12w -18
12w -18 what goes into 12w and -18? lets go with 2
2 (6w - 9) can 6w and -9 be factored more? yes by 3
2 x 3 (2w -3)
so
6 (2w -3)
