Sarah received \$55$55dollar sign, 55 for her birthday. She used some of that money to buy 333 shirts priced at mmm dollars each.
How much money does Sarah have left

The gades foundation and hbm corporation are eager to donate generously to their favorite charities. the gades foundation donated $250 in the first month, and each month afterward their cumulative donation total increases by 100$ the hbm corporation donated $64, in the first month, and each month afterward their cumulative donation total increases by 75%. in which month will the hbm corporation's cumulative donation total first exceed the gades foundations' cumulative donation total?

Can somebody me out with this question

Bring the fraction a/a-4 to a denominator of 16-a^2