Two Strings of Identical Material and Radius Are Stretched with the Same

Multiple Choice

Two strings of identical material and radius are stretched with the same tension with their ends fixed,but one string is 8.0 mm longer than the other.Waves on these strings propagate at 420 m/s.The fundamental frequency of the longer string is 528 Hz.What is the beat frequency when each string is vibrating at its fundamental frequency?

A) 22 Hz
B) 11 Hz
C) 16 Hz
D) 5.5 Hz
E) 27 Hz