for 0-10s, the car is slowing down but it is still accumulating distance so the distance increases at a slower rate. For 10-30s, the car is travelling at a constant speed so the distance increases at a constant rate. Then for 30-50s, it is similar to the case for 0-10s.

Thank you. May I check how did the solution get the points (10,400) and (30,800) and plot them in the graph?

Hi sry for the late comment, u need to calculate the area under the graph within the time span for each part