Use the Given Information to Find the Minimum Sample Size $\mu$

Multiple Choice

Use the given information to find the minimum sample size required to estimate an unknown population mean $\mu$
-How many women must be randomly selected to estimate the mean weight of women in one age group. We want 90% confidence that the sample mean is within 2.1 lb of the population mean, and the population standard
Deviation is known to be 19 lb.

A) 315
B) 278
C) 445
D) 222