Nelly needs to feed herself and her 14 friends, so she needs to buy enough pizza for 1 + 14 = 15 people.
Each pizza can feed 3 people, so Nelly needs to buy 15 / 3 = 5 pizzas.
Each pizza costs $12, so Nelly needs to spend 5 * $12 = $60 on pizza.
Nelly earns $4 per night babysitting, so she needs to babysit for $60 / $4 = 15 nights to afford the pizza.
#### 15
The answer is: 15
Below is a math problem. Provide a detailed, step-by-step solution.

### Problem:
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?

### Answer:
