you have eight machines operating independently. The mean production rate for each machine is 20.3 tons per day, and the standard deviation is 1.4 tons per day. Approximately how much uncertainty is there in the average daily production for the eight machines? Please report the usual summary measure

To estimate uncertainty you just use the two values given
Uncertainty=(avg+-standard deviation)

Since they all work independently each machine had the same uncertainty amount.

You can do the Leg work with the numbers it's very easy calculations.