12,16
12,18
8,18
16,14
The correct option is B (12,18)
For the observer detecting 480 Hz:
480 = 300 - v1 / 300 * 500
14400 = 150000 - 500v1
500v1 = 6000
v1 = 12 m/s
For the observer detecting 530 Hz:
530 = 300 + v2 / 300 * 500
159000 = 150000 + 500v2
500v2 = 9000
v2 = 18 m/s