Lets cut it diagonally into 2 triangles.
The diagonal length will be 7 x 2 = 14yd
Area of one triangle = 1/2 x 14 x 7 = 49 yd²
Area of the polygon = 2 x triangles
Area of the polygon = 2 x 49
Area of the polygon = 98 yd²
Answer: The regular polygon is 98 yd²