The scatter plot shows the relationship between the average number of nightly customers and the number of months since a restaurant opened. The equation represents the linear model for this data. y = 5x + 120

What does the number 5 in the equation mean in this context?

The restaurant has been open for 5 months.
For every 5 months the restaurant has been open, there are 120 more customers per night.
There were 5 customers per month after the restaurant was open 120 months.
The average number of customers per night increased by 5 each month.

There were 5 customers per night when the restaurant opened.