The rental rate for a cement mixer has a flat rate of $40 plus $20 for each day of the rental. The graph shows points representing the total cost of the rental.Which linear equation, in slope-intercept form, that models the total cost of the rental over time?
A. y = 50x + 25
B. y = 25x
C. y = 75x
D. y = x + 50
E. y = 20x +40