A vending machine was designed to dispense 7 ounces of INFO Cola into 8 ounce cups. For the machine, the amount of cola dispensed X, has a normal distribution. For these types of vending machines, the amount dispensed has an average variation (standard deviation) of 0.75 ounce. In order to see if the machine is working as designed, and to ensure consumer satisfaction, the mean amount of INFO Cola being dispensed is to be estimated. The amounts of cola dispensed into 100 cups were carefully measured and found to have a sample mean of 7.10 ounces.
The 90% confidence interval estimate for the true population mean amount of INFO Cola dispensed is:
a.(6.91, 7.29)
b.(6.92, 7.28)
c.(6.55, 7.65)
d.(6.83, 7.38)
e.(6.98, 7.22)
If somebody could show me the steps for how to solve this problem, I would really appreciate it. I feel like I am understanding the general concept, but there is some part I am missing when calculating the lower and upper limits for the interval that never ends up getting me to the final answer.