To calculate the wavelength, you will need to find the velocity of the wave and divide it by the frequency. Usually waves are measures in meters. So, the velocity is the speed of the wave. Frequency is usually measures in Hertz. This is equivalent to one second. Using the formula, you will then plug in the numbers of the frequency and wavespeed.

Once you calculate this, this will be the answer. Scientific notation should be used in order to make sure the answer is accurate. Since this is a photon, you will need to use another formula which is E = RE x (1/n21 – 1/n22). RE is equal to the Rydberg constant and n1 is the final energy level of the electron and n2 is the initial energy level of the electron.