An auto mechanic knows the average time it takes to replace a defective car radiator is 70 minutes with a standard deviation of 12 minutes. this average is based on a random sample of 50. which excel statements will construct a 90% confidence interval for the time needed to replace a defective car radiator? a. =70+1.96*12/sqrt(50), and =70-1.96*12/sqrt(50) b. =70+1.96*3.46/sqrt(50), and =70-1.96*3.46/sqrt(50) c. =70+1.645*3.46/sqrt(50), and =70-1.645*3.46/sqrt(50) d. =70+1.645*12/sqrt(50), and =70-1.645*12/sqrt(50) e. none of the above.