Charlie is re-landscaping his back yard and uses a coordinate plane to map the yard out. There is a pine tree located at (-5,5); the edge of a shed is located at (-5, 1) and the edge of a sandbox is located at (2,5). He plans to cover the triangular area formed by these three points with gravel. What area of the yard will be covered in gravel? Note: On the coordinate plane, each gridline represents 2 feet​