Use the syntactic sugar just learned about to convert the Area property to a single line property.

namespace Treehouse.CodeChallenges
{
    class Square : Polygon
    {
        public double SideLength { get; private set; }

        public double Area 
        { 
            get { return SideLength * SideLength; } 
        }

        public Square(double sideLength) : base(4)
        {
            SideLength = sideLength;
        }

        public void Scale(double factor)
        {
            SideLength *= factor;
        }
    }
}

namespace Treehouse.CodeChallenges
{
    class Polygon
    {
        public int NumSides { get; private set; }

        public Polygon(int numSides)
        {
            NumSides = numSides;
        }
    }
}