Calculation of the acceleration needed to overtake a runner

Mary and Sally are in a foot race. When Mary 22m from the finish line, she has a speed of 4.0m/s and is 5.0m behind Sally, who has a speed of 5.0m/s. Sally thinks she has an easy win and so, during the remaining portion of the race, decelerates at a constant rate of 0.50m/s2 to the finish line. What is the speed when Mary reach to the finish line?

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