First find the probability using the normal distirbution formula X - mean / standard deviation for both X = 350 and X =450 to get the values -1 and 1 so thi(-1) < P(Z) < thi(1) if you are familiar with normal distirbution table values you will calculate that the overall probability is 0.6827
knowing this we can roughly expect how much emergencies are in the response times by 0.6827 x 144 = 98