Let Δ ABC be the right triangle with AB = 18 and BC = 16. 18 * 16 / 2 = 144 u2
∠ADB = arctan(AB / BD) 77.471º
∠GDC = 180 - 77.471 = 102.529º
∠BCF = arctan(BF / BC) = 41.987º
3 more steps:
1/ Use the law of sines to calculate the length of a side GC
2/ Use trigonometry to calculate the height from D to GC
3/ Multiply side GC by the height and then divide by 2
Have fun! (btw, the answer is not 108)