(9c2−3cw−6w2)−(−9c2+9cw−w2)

The first thing you want to do is to add the [tex]9c^{2}[/tex] to the other one. You add instead of subtracting because the second one has a minus sign, and there is a minus sign in front of the parentheses. Two minus' make a plus. Adding these two together gives you a sum of [tex]18c^{2}[/tex].

Next, you want to simplify 9cw. Remember that since 9cw is positive, and there is a minus sign if front of the parentheses, you need to subtract here. Subtracting 3cw and 9cw gives you a difference of [tex]-12cw[/tex]. The new equation is [tex]18c^{2}-12cw[/tex].

Finally, we need to combine -w2 with -6w2. Remember that -w2 has a minus sign in front of it, so you need to add w2 to -6w2. This gives you [tex]-5c^{2}[/tex]. You combine this answer with the two answers above, and you get: [tex]18c^{2}-12cw-5w^{2}[/tex]. I hope this helps.