The number of gallons of water in a tank, y, over a period of x hours is shown in the graph below. What is...

5. The number of gallons of water in a tank, y, over a period of x hours is shown in the graph below.
What is the constant of proportionality in this situation?
A. 5 gallons per hour
B. 5 hours per gallon
C. 15 gallons per hour
D. 15 hours per gallon
6. The table below shows the amount of money in Lilly's bank account over time.
Which equation models the relationship between the age of Lilly's bank account, x, and the amount of money she has in her account, y?
A. y = 5x
B. y = 20x
C. y = 5x + 20
D. y = 20x + 5