Can someone help me w/a math problem?

Question

A processor of carrots cuts the green top off each carrot, washes the carrots, and inserts six to a package. Twenty packages are inserted in a box for shipment. To test the weight of the boxes, a few were checked. The mean weight was 20.4 pounds, the standard deviation 0.5 pounds. How many boxes must the processor sample to be 95 percent confident that the sample mean does not differ from the population mean by more than 0.2 pounds?

Answer 1

SAMPLE SIZE n = [(z-critical value * s)/B]^2 = [(1.96 * 0.5) / 0.2]^2 = 24 boxes