Astudent deposits the same amount of money into her bank account each week. at the end of the second week she has $30 in her account. at the end of the third week she has $45 in her account. how much will she have in her bank account at the end of the ninth week?

The student will have $135 in her bank account at the end of the ninth week. You can fine this out by finding out the amount she deposits a week and to do this you would take the $30 and divide it by 2 because she had $30 at the end of the second week. 
30/2=15
So you see that the student deposits $15 each week, so to find out how much money she will have in 9 weeks you will multiply her $15 by 9.
15x9=135
So the student will have $135 at the end of the ninth week. 

I'm gonna have to say about 13 percent

Wow. that is a really cool question.