I need help pls what is 900 pls 500

If the measure of xyz is 81 what is the measure of yz

The number of potato chips in a bag is normally distributed with a mean of 71 and a standard deviation of 2. approximately what percent of bags contain between 69 and 73 potato chips? approximately 68% approximately 71% approximately 95% approximately 99.7%

Ineed i been stuck on this question since yesterday