Wavelength, $$\lambda=\frac{c}{f}$$
Where, $$c=3\times10^8 \text{ m/s}$$ is the speed of light.
Substituting values, we get:
$$\lambda=\frac{3\times10^8 \text{ m/s}}{900\times10^6 \text{ Hz}}=\frac39 \text{ m}$$
$$\lambda=0.33 \text{ m}= 33\text{ cm}$$
Therefore, the wavelength is 33 cm.
