secondary 3 chevron_right A Maths chevron_right Singapore

This qn requires me to find the coordinates of D. BC is parallel to the x-axis and the coordinates of C is (4,2). The last part of the question, they give the area of the kite (28 units^2). I tried to find using gradient, getting the area of triangle ABC and so on but still couldn’t find the answer. Can anyone help me in this last part of the question? Thank you so much!