(a)
Speed is given by the slope of the distance-time graph. The more the angle made by the line of the positive slope with the x-axis, the more is the speed. From, the graph, B has the greatest slope and hence is moving fastest.
(b)
For the three objects to be at the same point at some time, the distance-time graph of all three particles should coincide at the same point at some time. Since this does not happen in the given graph, the particles do not coincide.
(c)
From the graph, B passes A after approximately 1 hr. At this time, the distance moved by C is 8 km.
(d)
From the graph, B passes C after approximately 0.6 hr. At this time, the distance moved by B is approximately 5.8 km.