A quality analyst wants to construct a sample mean chart for controlling a packaging process. He knows from past experience that whenever this process is in control, package weight is normally distributed with a mean of $20$ ounces and a standard deviation of two ounces. Each day last week, he randomly selected four packages and weighed each:

Day Weight $($ounces$)$

Monday $23222324$

Tuesday $23211921$

Wednesday $20192021$

Thursday $18192019$

Friday $18202220$

What is the mean of the sampling distribution of sample means when this process is in control?

Multiple Choice

$22$ ounces

$18$ ounces

$19$ ounces

$21$ ounces

$20$ ounces