You have to work backwards on this problem. 153.86 divided by 3.14 = 49. But 49 is only your diameter, so you have to divide by 2 to get radius. 49/2 = 24.5.
If you worked 19 hours per week at the cashier job, plus three hours a week doing swimming lessons, you'd be working 22 hours exactly, and making $214 per week. I hope this helps, and good luck! :)