When a sound wave travels from one medium to another, its frequency remains unchanged because frequency is a characteristic of the source. The velocity of a wave is related to its wavelength and frequency by the equation $v = f\lambda$. Therefore, for a constant frequency, the wavelength is directly proportional to the velocity ($\lambda \propto v$). Given: Velocity of sound in air, $v_{\text{air}} = 350 \text{ m/s}$ Velocity of sound in brass, $v_{\text{brass}} = 3500 \text{ m/s}$ The ratio of their velocities is: $\frac{v_{\text{brass}}}{v_{\text{air}}} = \frac{3500}{350} = 10$ Consequently, the ratio of their wavelengths will be: $\frac{\lambda_{\text{brass}}}{\lambda_{\text{air}}} = \frac{v_{\text{brass}}}{v_{\text{air}}} = 10$ Thus, the wavelength increases by a factor of $10$.