An ant is crawling down a tree at a rate of -8 millimeters per second. It passes through a big branch which we call position 0. Which equation represents the bug's position 9 seconds after it passes the branch?

a. -8 * -9 = 72
b. -8 * 9 = -72
c. -8 * 9 = 72
d. 8 * 9 = 72