There isn't a simple answer to that question.
Polly is going at a steady speed for the whole 5 seconds. She must have started before time-zero, because AT time-zero, she's already moving at 1m/s, and she stays at that steady speed for at least the next 5 seconds that we know of. (That's all the graph tells us.)
Art is standing at the starting line, waiting for the signal to GO. At time zero, he's not moving at all, so Polly is moving faster than he is.
At time-zero, (when the starter fires the pistol ?), Art starts moving AND building up speed. He builds up speed steadily, going faster and faster. His speed builds and builds all the way across the graph. He starts out with zero speed, and he accelerates so that his speed grows by 1 m/s every 2 sec. After 2 sec, he's moving at 1 m/s, and after 4 sec, he's built it up to 2 m/s.
Polly is moving at 1 m/s all across the graph, for the whole 5 sec. So she's going faster than Art is, for the first 2 seconds. But Art is building his speed, faster and faster. He reaches 1 m/s after 2 sec, and after that he's going faster that Polly.
All this information that I'm saying is on the graph. I'm just describing the graph in painful boring detail. As you read my description, you should be able to look over at the graph every time I say something, and see it there.
