If she charges 4.50 per hour and she babysits for 11 to 16 hours per week, then multiply 4.50 by both 11 and 16.
4.50*11=49.5
4.50*16=72
So she makes between 49.5 and 72 dollars per week. If we average the two numbers, then she makes about 60.75 dollars per week. If we divide 147 by 60.75, then the answer is 2.42, meaning Carla should be able to get the bike in about 2 and a half weeks!