Jim washes cars to earn money. On monday he washes 12 cars and earns $84. On tuesday he washes 6 cars and earns $42. On wednesday he washes 15 cars and earns $105. What is the rate of change of Jim's earnings?

Me with this assignment ! i only partially understand, so explain. also it's a work sample. at the championship bike race, steve and paula were fighting for first place. steve was 175 feet ahead of paula and had only 300 feet left to go. he was very tired and was going only 9 feet per second. paula was desperate to catch up and was going 15 feet per second. who won the bike race and by how far did she/he win?