An equation of a function y(t) is shown.
y(t)=−t²+14t−40

Which of the following statements are true about the graph of y(t) for
6≤t≤8 and WHY?

a. The value of y(t) increases over the interval 6≤t≤7

b. The value of y(t) increases over the interval 7≤t≤8

c. The average rate of change over the interval 6≤t≤8 is 0

d. The value of y(t) is constant over the interval 6≤t≤8

e. The average rate of changer over the interval 6≤t≤7 is the same as the average rate of change over the interval 7≤t≤8