A garden shop sells 15​" by 15​" square stepping stones for the same price as 20​" round stones. If all stepping stones are the same​ thickness, which option gives the most rock for the​ money?

The area of a square stepping stone is ( ? ) in.2 and the area of a round stepping stone is ( ? ) in.2​, so the option that gives the most rock for the money is the (round or square)?