According to Pythagoras' law, AC? =AB？ +BC？

AC=√(3？ +4? )=5

CD= 12，AD= 13，AC？ +CD？ =5? + 12? = 169= 13? =AD？

Then △ACD is a right triangle, ∠ C = 90.

S△ABC= 1/2(AB×BC)=6

S△ACD= 1/2(AC×CD)=30

Total area =30+6=36