Please help me me and my friends don’t get it

What is the frequency of the sinusoidal graph?

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.

Rose bought a new hat when she was on vacation. the following formula describes the percent sales tax rose paid b=t-c/c