An electron and a proton each move at 3.0 × 10⁶ m s⁻¹.

Step 1. Electron. $\dfrac{6.626 \times 10^{-34}}{9.109 \times 10^{-31} \times 3.0 \times 10^{6}} = 2.42 \times 10^{-10}\ \text{m}$.

Step 2. Proton. $\dfrac{6.626 \times 10^{-34}}{1.673 \times 10^{-27} \times 3.0 \times 10^{6}} = 1.32 \times 10^{-13}\ \text{m}$.

Step 3. Ratio. $\dfrac{m_p}{m_e} = 1837$: the electron's wavelength is $1837$ times longer.