PLEASE HELP I DONT UNDERSTAND

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?

X+y=-4 x-y=2 use elimination with adding and subtraction

Item 1 solve for s. s+24=90 −114 −66 66 114