A construction zone on a highway has a posted speed limit of 40 kms per hour. The speeds of vehicles passing through this construction zone are normally distributed with a mean of 46 kms per hour and...

A construction zone on a highway has a posted speed limit of 40 kms per hour. The speeds of vehicles passing through this construction zone are normally distributed with a mean of 46 kms per hour and a
standard deviation of 4 kms per hour. Find the percentage of vehicles passing through this construction zone that are

a. exceeding the posted speed limit
b. traveling at speeds between 50 and 57 kms per hour