Aziz is a watermelon vendor. He finds that the average weight of watermelons is 15 lbs, with a standard deviation of 6 lbs. Let X be the random variable of a watermelon's weight. Assume that the weights of the watermelons he sells are normally distributed. You may round your final answers to 3 decimal places.

a)What is the probability that Aziz sells a watermelon weighing between 13 and 16 lbs?

b) Suppose k is a constant such that P(X>k)=0.06 . Find k

c)If the standard deviation is doubled, what is the new probability that he sells a watermelon between 13 lbs and 16 lbs?