Does anyone know how to solve special right triangles,and give me an complete answer and show all work please!?

The problem is:If x=3 radical 3 and find "a" and CD.The right triangle is a 30,60,90 triangle. The angles of the triangle are ABC also D is the altitude from the right angle and to the hypotenuse. So please help I don't get it at all.THANK YOU!