The equation you have is correct. To solve the next ones you use that equation and plug in the number of hours given. So for 31 hours of babysitting you’d do this: 12(32)+15c=420 384+15c=420 15c=36 c=2.4
Same thing for 10 hours babysitting 12(10)+15c=420 120+15c=420 15c=300 c=20
