Note: 1(c) is incorrect in these solutions! For speeding up, the velocity and acceleration are in the same direction, i.e. they have the same sign. So the answer should be t > 6 and 2 < t < 4 for speeding up. This makes sense: speeding up should occur after the particle has come to a stop (at t=2 and t=6), regardless of whether there is a local max or min for velocity at these times.
Also, note that problem 3 *is* on our exam, contrary to these old solutions from a previous semester. Please ask your instructor or TA if you are unsure what the solution is.