D (-1/2, 5/2), E (7, 3) and F (7/2, 7/2) are the midpoints of sides AB, BC and CA respectively. ABC is a triangle.
Area of triangle DEF :
The triangles ADE, BDF, DEF, EFC are all of equal size. The reason is DE = 1/2 BC and Δ ADE is similar to Δ ABC. Hence, area of Δ ADE = 1/4 * area of Δ ABC.
So area of Δ ABC = 57/2