The graph below shows the height of Cindy's model rocket during the course of its flight. Flight of Cindy's Rocket

Height (in feet)
y
22
20
18
16
14
12
10
6
4.
2.
x 0 1 2 3 4 5 6 7 8 9
Time (in seconds)
Which of these equations can be used to find the height of the rocket at any time during its flight?
A. y = 9x
B. y = x^2 - 81
C. y = -x^2 + 9x
D. y = 9 - 9x^2