Resultant is the correct answer!
Refer to the diagram shown below.
In 2.4 hours, the distance traveled by the first airplane heading a 51.3° at 750 mph is
a = 750*2.4 = 1800 miles.
The second airplane travels
b = 620*2.4 = 1488 mile
The angle between the two airplanes is
163° - 51.3° = 111.7°
Let c = the distance between the two airplanes after 2.4 hours.
From the Law of Cosines, obtain
c² = a² + b² - 2ab cos(111.7°)
= 3.24 x 10⁶ + 2.2141 x 10⁶
c = 2335.41 miles
Answer: 2335.4 miles
It is called condensation. Hope this helped!
See the attached picture: