A random sample of size n1 = 16 is selected from a normal population with a mean of 75 and standard deviation of 8. A second random sample of size n2 = 9 is taken independently from another normal population with mean 70 and standard deviation of 12. Let X1 and X2 be the two sample means. Find(a) The probability that X1 − X2 exceeds 4.(b) The probability that 3.5 < X1 − X2 < 5.5.