Below is an instruction that describes a task. Write a response that appropriately completes the request in English. Please answer in English.

### Instruction:
Nelly wants to buy pizza for herself and her 14 friends. Each pizza costs $12 and can feed 3 people. If Nelly earns $4 a night babysitting the neighbors' kids, how many nights will she have to babysit to afford the pizza?

### Response:
There are 15 - 1 = <<15-1=14>>14 friends.
She needs to buy 15 / 3 = <<15/3=5>>5 pizzas.
The pizza will cost $12 x 5 = $<<12*5=60>>60.
It will take her $60 / $4 = <<60/4=15>>15 nights worth of babysitting to afford the pizza.
#### 15