First you need to find out how much the driver makes for the normal 10 lap event. $20 per lap for 10 laps is $200.
Now the driver earns 3x that amount for every lap over the normal 10 laps. So for every extra lap, the driver earns $600. Five extra laps would give him $3000.
So for the total 15 laps the drive would earn the initial $200 plus the extra $3000 or $3200 total.
