When a woman learns she is pregnant, her doctor usually calculates a "due date" for the baby. Actual lengths of pregnancy terms are nearly normally distributed around the due date (mean) with a standard deviation of 15 days.

a. Construct a normal distribution curve modeling the problem

b. About what percentage of births occur within 30 days before the due date?

c. About what percentage of births occur less than 15 days before or after the due date?

d. About what percentages of births occur after day 12? Describe or include a picture of how the answer was obtained.