A survey of 144 retail stores revealed that the average price of a DVD was $375 with a standard error of $20.

Reference: Ref. 9-4

What is the 95% confidence interval to estimate the true cost of the DVD?

a. $323.40 to $426.60

b. $328.40 to $421.60

c. $335.00 to $415.00

d. $335.80 to $414.20