It is 2020,What year would the next harvest moon be?Also when is the next blue moon as well?(Btw this is and addition problem)

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.