Answer
$$\therefore \lambda = 3.3\times 10^{-14}\text{ m}$$
Work Step by Step
De Broglie Wavelength of a particle of mass $m$ moving with velocity $v$ is given by:
$$\lambda = \frac{h}{mv}$$
where
$m = 4.00 \text{ amu }=4.00\times 1.67\times 10^{-27} \text{ kg}$
$v = 3.0\times 10^{6}\text{ m/s}$
$$\therefore \lambda = \frac{6.67\times 10^{-34}}{1.67\times 10^{-27}\times 3\times 10^6}m = 3.3\times 10^{-14}\text{ m}$$
