Question

The two strings have the same tension and mass per unit length, but they differ in length by 0.54 cm. The waves on the shorter string propagate with a speed of 41.7 m/s, and the fundamental frequency of the shorter string is 227 Hz. Determine the beat frequency produced by the two standing waves.

I thought that for beat frequency you could do f1 - f2 but there is only obe value of Hz so now I am stuck.