I am giving you the steps
1) Plot a rough diagram with the given coordinates.
2) Draw one diagonal of the quadrilateral of the Quadrilateral formed.
3) Observe the triangles formed and their coordinates.
4) Find the area of those two triangles by the the formula : s(s-a)(s-b)(s-c)/2
where s = perimeter of triangle/2 and a,b,c are the respective sides of the triangle.
5) Add those two areas obtained to get the area of the Quadrilateral.