Using it's concept, it is found that the sample mean package weight for Thursday is of 19 ounces.
The mean of a data-set is given by the sum of the observations divided by the number of observations.
For Thursday, the package weights in ounces are given by: {18, 19, 20, 19}.
Hence, the sample mean in ounces is of:
M = (18 + 19 + 20 + 19)/4 = 19.
More can be learned about the mean concept at https://brainly.com/question/24628525