I am gonna do what you did to me and say its easy.
N = 2424 is the sample size (amount of cars being sampled)
df = degrees of freedom
df = n-1
df = 2424-1
df = 2423
Side Note: if there is a typo and the sample size should be n = 24 (instead of 2424), then the df would be df = n-1=24-1 = 23
You need to set up a linear graph. One side with gallons and the other with dollars. Point 1 will be at (1500, 2.10). Point 2 (1300, 2.95). Draw a straight line through these points in your graph and your graph will then give you the answers to your other questions.
1/3 is the answer. Hope this helps
