A sonometer wire of fixed length is stretched by a tension T1 and vibrates in its fundamental. When sounded with a tuning fork, 6 beats per second are heard. The tension is then increased to 1.21T1, making the note of the wire higher, and the beat frequency becomes 2 beats per second. The frequency of the tuning fork is
a) 80Hz
b) 86Hz
c) 74Hz
d) 90Hz