The distribution of passenger vehicle speeds traveling on the Interstate 5 Freeway (I-5) in California is nearly normal with a mean of 72.6 miles/hour an a standard deviation of 4.78 miles/hour

a. what percent of passenger vehicles travel slower than 80 miles/hour?

b. what percent of passenger vehicles travel between 60 and 80 miles/hour?

c. how fast do the fastest 5% of passenger vehicles travel?

d. the speed limit on this stretch of the I-5 is 70 miles/hour. Approximate what percentage of the passenger vehicles travel above the speed limit on this stretch of the I-5.