How Many Tissues Should a Package of Tissues Contain? Researchers $\bar { x } = 45 , s = 18$

How many tissues should a package of tissues contain? Researchers have determined that a person uses an average of 50 tissues during a cold. Suppose a random sample of 10,000 people yielded the following data on the number of tissues used during a cold: $\bar { x } = 45 , s = 18$ . Using the sample information provided, set up the calculation for the test statistic for the relevant hypothesis test, but do not simplify.
A) $z = \frac { 45 - 50 } { \frac { 18 } { \sqrt { 10,000 } } }$

B) $z = \frac { 45 - 50 } { 18 }$

C) $z=\frac{45-50}{\frac{18}{10,000^{2}}}$

D) $z = \frac { 45 - 50 } { \frac { 18 ^ { 2 } } { 10,000 } }$