So:

*V (in dollars) stands for the depreciated or non depreciated value of the jet ski.
*t (in years) stands for the amount of time that has passed. t is greater or equal to 0 and less than or equal to 11.
-------------------
Question (a):
Now V is a function of t. V=f(t).
When t=0, V=0 --> Point:(0,0)
When t=2, V=6550 --> Point (2, 6550)
When t=4, V=5100 --> Point (4, 5100)
When t=6, V=3650 --> Point (6, 3650)
When t=8, V=2200 --> Point (8,2200)
When t=11, V=25 --> Point: (11, 25)
So as the graph V=8000-725t is LINEAR, we can draw a line through the points mentioned above.------------------------
Question (b): After how many years will the jet ski be worth $5100?
Answer: 4 years.-----------------------
Question (c): What will be the value of the jet ski after 9 years?
The answer is $1,475.00