buted with mean u= 290 days and standard deviation 0= 20 days.(a) What is the probablity that a randomly selected preganancy lasts less than 284 days?

Suppose the lengths of the pregnancies of a certain animal are approximately normally distributed with mean u= 290 days and standard deviation 0= 20 days.(a) What is the probablity that a randomly selected preganancy lasts less than 284 days?