∠ FBC = 30 (known)

∠ABC=60

∠A=30

AB = 2bd (the right-angled side opposite to the 30-degree angle is half of the hypotenuse)

AB=220BD= 1 10？ Ad = 1 10√3 with Pythagorean theorem

12-110 √ 3/20 < 4, so it will not be affected by typhoon.