How in the world do you do this????

Career Mode, SD-75- Held up by the Highway scenario, 20 mph speed zones. It says medium difficulty (
)
I can have 90% brakes on and speed is still climbing, I throw it in reverse and give it 13% power, works for a bit and the speed goes up past 20 mph. I come to almost a complete stop, but the speedometer says I'm doing 15mph
I finally finished the mission at -1021 pts.
Any tips from you experts?

I can have 90% brakes on and speed is still climbing, I throw it in reverse and give it 13% power, works for a bit and the speed goes up past 20 mph. I come to almost a complete stop, but the speedometer says I'm doing 15mph


I finally finished the mission at -1021 pts.
Any tips from you experts?