Calculating wavelength of sine wave
The wavelength is $$\lambda = \frac{v}{f}$$

where \$v\$ is the velocity of the wave and \$f\$ is the frequency. Here you have $$v = \frac{2500\text{m}}{3.3\mu\text{s}}$$

Just be sure to convert \$v\$ to m/s and \$f\$ to Hz so the units work out. \$\lambda\$ is in meters.