You get paid $10 an hour. In order to make $210, you need to work 21 hours. If you work the same amount of hours for four days a
nd you work the remaining hours on the fifth day, how many hours do you have to work for each of the four days and how many will you have left to work on the fifth day?
If you want to make it so that you work most of the hours on the first 4 days, you should work 5 hours. 5*4=20, so 1 hour would be left over on the 5th day.