If x-y=10 and x+y=20 what is the answer for x^2-y^2?

Alonso walked with his friend andy one day, and wanted to compare their speeds. alonso walked 3 miles in one hour, and andy walked 2 miles in 2 hours. complete the table to graph the relationship for each person.

This is about circle theorems. someone asap : (

How many quarts of a 50% solution of acid must be added to 20 quarts of a 20% solution of acid in order to get a 40% solution of acid?