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4. Suppose a skydiver leaps from a plane and falls in a straight line. She falls at a terminal velocity of 80 meters per second for 19 seconds, at which time she opens her parachute. The velocity decreases linearly to 6 meters per second over a two-second period and then remains constant until she reaches the ground at t = 40 seconds. The motion is described by the velocity function, v(t). 80 if Ost