Janie is walking in a walk-a-thon to earn money for charity. She walks at a constant rate and for every hour that she walks she makes money. She models her earnings by a linear equation since she is walking at a constant rate. The x-axis shows the amount of time she walks in hours and the y-axis shows the amount of money she earns in tens of dollars.
How much will she earn if she walks for four hours?
A) $4
B) $8
C) $40
D) $80
