HELP ASAP PLEASE!!!!!!!

The graph below represents the price of sending text messages using the services of a phone company. What is the constant of proportionality? A graph is shown. The values on the x axis are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. The values on the y axis are 0, 8, 16, 24, 32, 40, 48, 56, 64, 72, 80. Points are shown on ordered pairs 0, 0 and 2, 16 and 4, 32 and 6, 48 and 8, 64. These points are connected by a line. The label on the x axis is Text Messages Sent. The label on the y axis is Price in cents.
A.8
B.14
C.16
D.48