HELP please, will give brainily

You have 3 boxes, one "strawberries"; one "mentos" and one "mixed".but you know that all the labels are in incorrect order .how do you know witch is witch?

Scores on the cognitive scale of the bayley-scales of infant and toddler development range from 1 to 19, with a standard deviation of 3. calculate the margin of error in estimating the true mean cognitive scale score, with 99% confidence, if there are 12 infants and toddlers in a sample.

What is the missing reason in the proof? segment addition congruent segments theorem transitive property of equality subtraction property of equality?