
Hi Rebeck and Chandan 2. It's simply two 306090 triangles. Initially the side opposite to 30 degree is 100 km that means the hypotenuse i.e. distance between the aircrafts is 2*100 = 200 km initially.After half an hour, the side opposite to 60 degree is 100 km that means the hypotenuse i.e. distance between the aircrafts will be 200/3^{0.5} ~ 115.47 km. Kamal Lohia
