Need help with this problem

Me with this one question, and i'll upvote the brainliest answer

To solve the system of equations below, pedro isolated the variable y in the first equation and then substituted it into the second equation. what was the resulting equation? { 5y=10x {x^2+y^2=36

Robert is placing sod in two square shaped areas of his backyard. one side of the first area is 7.5 feet. one side of the other area is 5.7 feet. the sod costs y dollars per square foot