Attempting to stop on a slippery road, a car moving at 90 km/h skids across the road at a 30 degrees angle to its initial motion, coming to a stop in 3.9s. Determine the average acceleration in m/s^2 (meter per second square), using a coordinate system with the x axis in the direction of the car's original motion and the y axis toward the side of the road to which the car skids.