A man is pacing back and forth along a straight line. The man's velocity can be modeled by v(t) = 2.31n (3+2t) - feet per minute for 0t 120 minutes. (a) Find the acceleration of the man at t = 20 minutes. (b) Find the time at which the man is stopped. At this time, how far is the man from the point at which he started? (c) Write, but do not solve, an equation including one or more integrals to find the time t = k at which the man returns to his starting point.