Just compare it as a regular graph.:)
We know that the load is 8713 lbs.
The total weight (truck + load) is 17200 lb.
Then, we can calculate the weight of the empty truck as:

Answer: the empty truck's weight is 8487 lb.
T: empty truck's weight
W: total weight (loaded truck's weight)
L: Load
The equation is:
T = W - L
Answer: 1) Check if the inputs and outputs doesn't fail the vertical line test. 2) Check if every input has exactly on output. 3) Check if is a linear function.
Step-by-step explanation: