What is critical value as well please.

The birth weights for two groups of babies were compared in a study. In one group the mothers took a zinc supplement during pregnancy. In another group, the mothers took a placebo. A sample of 134 babies in the zinc group had a mean birth weight of 3049 grams. A sample of 142 babies in the placebo group had a mean birth weight of 3081 grams. Assume that the population standard deviation for the zinc group is 613 grams, while the population standard deviation for the placebo group is 667 grams. Determine the 90 % confidence interval for the true difference between the mean birth weights for "zinc" babies versus "placebo" babies. Step 2 of 2: Construct the 90 % confidence interval, Round your answers to the nearest whole number