JEE Main 2019 Physics question

Two cars A and B are moving away from each other in opposite directions. Both the cars are moving with a speed of 20 ms with respect to the ground. If an observer in car A detects a frequency 2000 Hz of the sound coming from car B, what is the natural frequency of the sound source in car B? (speed of sound in air = 340 ms)

• (A)2060 Hz
• (B)2150 Hz
• (C)2300 Hz
• (D)2250 HzCorrect