Answers:

1.      Carla gets paid the least for each additional pizza. 

The graph of her earnings has the smallest slope - the line increases at the smallest rate.

2.      Carla -- $1 per pizza

      Drey -- $2 per pizza

      Robert -- $3 per pizza

3.      Drey and Carla will be paid equal amounts when they both sell 7 pizzas.

4.      The y-intercepts tell you how much each person gets paid before they sells any pizzas.

5.      Carla’s pay plan is the best if only four or less pizzas are sold.

6.      Robert’s pay plan is the best when 12 or more pizzas are delivered. 

This is because the slope of his line increases at the highest rate.