You are driving your 1800 kg car at 25 m/s over a circular hill that has a radius of 150 m. A deer running across the road causes you to hit the brakes hard while right at the summit of the hill, and you start to skid. The coefficient of kinetic friction between your tires and the road is 0.75. What is the magnitude of your horizontal acceleration as you begin to slow? Express your answer with the appropriate units.

a = ?