Two piano strings are supposed to be vibrating at 132 Hz, but a piano tuner hears three

Question:

Two piano strings are supposed to be vibrating at 132 Hz, but a piano tuner hears three beats every 2.0s when they are played together.
(a) If one is vibrating at 132 Hz, what must be the frequency of the other (is there only one answer)?
(b) By how much (in percent) must the tension be increased or decreased to bring them in tune?