A speed trap is set up with two pressure-activated strips placed across a highway, 116 m apart. A car is speeding along at 31.5 m/s, while the speed limit is 21 m/s. At the instant the car activates the first strip, the driver begins slowing down. What minimum deceleration is needed in order that the average speed is within the limit by the time the car crosses the second marker? I have no clue on what equation to use to solve this problem or how I would go about solving this problem. Can someone please help me?