Evan has agreed to mow his neighbor's lawn each week. His neighbor will pay him $15 each week. Evan will also baby-sit some hours each week for $10 per hour. Evan needs to make at least $100 per week to save for his own car, but if he makes $200 or more each week his parents will charge him rent. How many hours h should Evan agree to baby-sit each week to avoid paying rent but still be able to save for his car?