What doexs this equal: 3ab-9ab+7ab

I think that it equals 1ab. Because 3ab - 9ab = - 6ab + 7ab = 1ab

So, this question tests wether or not you know how to combing "like terms".

Like terms are terms (thing inbetween + or-) that have the same variables.

Since all three terms contain "ab" we can add and subtract them.

So, 3ab-9ab = - 6ab

-6ab+7ab=1ab

1ab is the correct answers