In a resonance tube experiment a fork of 512 Hz gives the first resonance at 15.9 cm and the second…

(a) $\lambda = 2(49.5\ \text{cm} - 15.9\ \text{cm}) = 67.2\ \text{cm}$.

(b) $v = f\lambda = 512\ \text{Hz} \times 0.672\ \text{m} = 344\ \text{m/s}$.

(c) $e = \dfrac{49.5\ \text{cm} - 3 \times 15.9\ \text{cm}}{2} = \dfrac{49.5\ \text{cm} - 47.7\ \text{cm}}{2} = 0.9\ \text{cm}$.