Please help me I hate math

9/10 divide by -3/15 as a mixed number

How long must $542 be invested at a rate of 7% to earn $303.52 in interest? in a easier way

Dean and karlene get paid to write songs. dean is paid a one-time fee of $20 plus $80 per day. karlene is paid a one-time fee of $25 plus $100 per day. write an expression to represent how much a producer will pay to hire both to work the same number of days on a song.