The Picture on the Right Represents the Wavefronts of a Supersonic

Multiple Choice

The picture on the right represents the wavefronts of a supersonic flight.The angle $\theta$ = 40 ^$\circ$ .If the speed of sound is 300 m/s,what is the speed of the plane?

A) 360 m/s
B) 330 m/s
C) 300 m/s
D) 390 m/s
E) 470 m/s