4x15=60
60-16=44
It is 4 times 15 because if there are 4 bike racks and each bike racks have 15 slots for bikes then you have to multiply the amount of slots with the amount of bike racks are available, then you must find out how many slots are left. To do this you must subtract the amount of bikes in the bike racks with the total amount of slots. This will leave you with 44 slots available.
