10th grade Geometry Problem in IIT JEE 2007 Advanced MCQ, , Area of quadrilateral, Tangent, circle

This MCQ question was asked in IITJEE 2007 from 10th grade Geometry. The question is as following : ABCD is a quadrilateral with area 18 cm2. AB, , CD and AB 2CD, AD is perpendicular to CD. A circle touches all the four sides of the quadrilateral ABCD. What is the radius of the , IITJEE, ,JEEMAINS, ,JEEADVANCED, ,NTSE, ,SSC, ,NDA, ,SSC