Mary has had five unit tests in math so far this semester. she has achieved scores

Mary has had five unit tests in math so far this semester.
she has achieved scores of 86, 82, 93, 88, and 89 out of 100.
she knows there are only two unit tests left, and would like to achieve an overall average of 90 on the seven tests.
a) can she achieve her desired average? if so, what average would she need to achieve on the last two tests?
b) what is the minimum score she could get on either of the last two tests, and still achieve an overall average of 90?