The answer they are looking for is the last one. However the last two are technically correct but the third one would result in negative work.
Answer:

Explanation:
given,
Speed of sound = 343 m/s
frequency of horn = 260 Hz
the friend is approaching, the frequency is increased by the Doppler Effect. The frequency is 266 Hz
using formula





the speed of friends approaching is equal to 
Answer:
The answer you would be looking for is A.
Explanation: