area of a convex quadrilateral I have a quadrilateral with sides as follows: $30, 20, 30, 15.$ 
I do not have any other information about the quadrilateral apart from this.
Is it possible to calculate its area?

A quadrilateral with sides $30,20,30,15?$ two sides are equal, right? Why don't you try to draw it? Divide it into two triangles. If the two equal sides have a common edge, one of the triangles is isosceles, i.e. has equal angles. Can you find the rest of the angles and the area?
