A 0.25-m string, vibrating in its sixth harmonic, excites a 0.96-m pipe that is open at both ends into its second overtone resonance. The speed of sound in air is 345 m/s. The common resonant frequency of the string and the pipe is closest to
Answer please with procedure

a. 630 Hz.
b. 450 Hz.
c. 700 Hz.
d. 540 Hz.
e. 360 Hz.