Milly's babysitter charges $16/hour. Milly is considering switching to a new babysitter who charges $12/hour, but also charges an extra $3 for each time the kids scream at her. If Milly usually hires the babysitter for 6 hours, and her kids usually scream twice per babysitting gig, how much less will the new babysitter cost? Let's be accurate as possible.
First figure out how much the first babysitter costs by multiplying her hourly rate by the number of hours she works: $16 / hour * 6 hours = $96. Then use the same method to figure out how much the second babysitter charges before any screaming: $12 / hour * 6 hours = $72. Then figure out how much the babysitter charges for two screams: 2 screams * $3 / scream = $6. Finally, subtract the second babysitter's two charges from the first babysitter's total charge to find the difference: $96 - $72 - $6 = $18.
The answer: 18.