Drawing the velocity-time graph should reveal:

1) The first 10 seconds shows the car overtaking the motorcycle. Assuming a constant acceleration, the distance gained (area between two curves) is:

(I have converted the speed into SI units in this single step as well)

2) The next 5 seconds (t=10 to t=15) shows the motorcycle catching up to the car in distance (it's speed is now faster than the car). Assuming constant acceleration again, the distance caught up (area between two curves) is:

So now, the car is only ahead of the motorcycle by 97.2 metres, and the car is catching up at a rate of

.

This means that it will take another

for the motorcycle to catch up.

This means the total time taken (including the initial 15 seconds we did manually) is

.