a. The area under the curve for the car (represented by the red line) at time t is simply 72t. (It is a rectangle, 72 high and t width).

The area under the trapezium for the police car (represented by the blue line) at unknown time t is:

1/2 (t + t - 10) × 90 = 45 (2t - 10)

These are equal when 72t = 45 (2t - 10)

That is, when 72t = 90t - 450

So t = 25 s

b. Both of the cars have travelled 72 × (25/3600) × 1000 = 500m