A violinist tuning her instrument to a piano note of 264 Hz detects three beats per second.

Question:

A violinist tuning her instrument to a piano note of 264 Hz detects three beats per second.
(a) The frequency of the violin could be (1) less than 264 Hz, (2) equal to 264 Hz, (3) greater than 264 Hz, (4) both (1) and (3). Why?
(b) What are the possible frequencies of the violin tone?