SAT problem solving practice test 01

10.In the figure above AD = 4, AB = 3 and CD = 9. What is the area of triangle AEC ?

A. 18

B. 13.5

C. 9

D. 4.5

E. 3

you can go to the site above for an image it would not paste into here and the program wouldnt allow me to add a photo saved from the site

the answer is 4.5 but i cannot for the life of me recall how to do this.