$15 to $20 find the percent change then round to the nearest percent​

Ijust need to see how to do this. so you don’t have to answer all of them just a step by step explanation of one.

Players on the school soccer team are selling candles to raise money for an upcoming trip. each player has 24 candles to sell. if a player sells 4 candles a profit of$30 is made. if he sells 12 candles a profit of $70 is made. determine an equation to model his situation?

With both problems. a.s.a.p directions on photo ^