Use the given lengths of the three sides and cosine rule to find the length of the fourth side. Let us call this length ddd.
Then use Heron's formula to calculate the area: A=(s−a)(s−b)(s−c)(s−d)A = \sqrt{(s-a)(s-b)(s-c)(s-d)}A=(s−a)(s−b)(s−c)(s−d)
Here, sss is the semi-perimeter of the quadrilateral.