Let d(x) denote Sergio's distance (in meters) from the starting line x seconds after the race started. If v is his max speed, then Sergio's displacement after 7 seconds is v(x - 7). Thus, d(x) - 35 = v(x - 7) for x >= 7. Since d = 70 when t = 12, we find 70 - 35 = v(12 - 7), or 35 = 5v. Therefore, v = 7 meters per second and

d(x) = 35 + 7(x - 7), x >= 7

During the additional z seconds, Sergio will travel 7z meters. His distance from the starting line 7 + z seconds after the race has started is 35 + 7z.

MARK A.

what do they mean by "z" seconds, how is that calculated?08/28/19