Really struggling with this one.

Really struggling with this one. Any help would be greatly appreciated. Thx!

The inspection division of the Lee County Weights and Measures Department is interested in estimating the actual amount of soft drink that is placed in 2-liter bottles at the local bottling plant of a large nationally known soft-drink company. The bottling plant has informed the inspection division that the standard deviation for 2-liter bottles is 0.05 liter. A random sample of one hundred 2-liter bottles obtained from this bottling plant indicates a sample average of 1.99 liters. Set up a 95% confidence interval estimate of the true average amount of soft drink in each bottle.