If an open organ pipe is sounded with a tuning fork having frequency $256 \mathrm{~Hz}$, resonance occurs at $35 \mathrm{~cm}$ and $105 \mathrm{~cm}$, the velocity of sound is
(a) $360 \mathrm{~m} / \mathrm{s}$
(b) $512 \mathrm{~m} / \mathrm{s}$
(c) $524 \mathrm{~m} / \mathrm{s}$
(d) all of these