The rate of change is shown to the right of the second graph as being -2
At 5 to 6 the average rate of change is -11, so at 6 to 7 the rate of change would be -11-2 = -13, then from 7 to 8 it would be -13-2 = -15.
The answer is D. -15
A random supporter roots the home team with probability 0.9, and the away team with probability 0.1.
Choosing 6 out of 8 supporters who root for the home team has probability

multiply the price by the discount then subtract the answer from the price
4 * 0.20 = 0.80
4-0.80 = 3.20
sale price is $3.20