Answer:
3.1 * 10^-19 joules
Step-by-step explanation:
The equation you want to use is:
E=hc/lambda (lambda = wavelength).
It might also be given to you in the form:
E=constant/wavelength
since h = 6.626*10^-34, c = 2.998*10^8, and the wavelength is 6.4*10^7, the values can be plugged into the equation to solve for the energy.
E=(6.626*10^-34 * 2.998*10^8) / (6.4*10^-7) = 3.1 * 10^-19 joules