#### Answer

The concave quadrilateral ABCD has interiors angles with a sum of 360$^{\circ}$ because it is made up of two triangles whose sum of interior angles are always $180^{\circ}$.

#### Work Step by Step

Draw a line from B to D to form triangles BCD and ABD. Add the interior angles of each (180+180) to equal 360 for the total sum of the measures of the interior angles of the quadrilateral.