A particle moves along a straight line. The graph of the particle's velocity v(t) at time t is shown above for 0 ≤ t ≤ m, where j, k, l, and m are constants. The graph intersects the horizontal axis at t = 0, t = k, and t = m and has horizontal tangents at t = j and t = l. For what values of t is the speed of the particle increasing?