Mary has 1/4 of a tank of gas. a quarter or a tank is equal to 5 gallons how many gallons does her tank hold

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?

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?

Could somebody me with this radical simplification?