Mifrin, the manufacturer of an over-the-counter pain reliever, claims that its product brings relief to headache sufferers in less than 3.5 minutes, on average. To make this claim in its commercials, Mifrin was required to show evidence that headache relief really did come in less than 3.5 minutes, on average. Mifrin reported that for a random sample of 50 headache sufferers, the mean time to relief was 3.3 minutes and the standard deviation was 60 seconds. You would like to estimate the average time it takes for headache sufferers to feel relief after taking Mifrin. Which of the following would you use to calculate the 99% confidence interval? a. z = ±2.300
b. z = ±2.575
c. t = ±2.678
d. t = ±2.403