In 1974 a Radio Signal Was Sent from the Arecibo

In 1974 a radio signal was sent from the Arecibo radio telescope toward the globular cluster M13, which is about 6.8 kpc distant. How long will it take this signal to reach M13?

A) 6800 years
B) 13,600 years
C) 22,200 years
D) 44,400 years