1 A = 1.0 X 10^-10 meters, so... I'll show you this way to get energy

6573 A (1.0 X 10^-10 meter/1 A) = 6.573 X 10^-7 meters

Energy = Planck's constant * speed of light m/s/ wavelength in meters

E = (6.626 X 10^-34 J*s)(2.998 X 10^8 m/s)/(6.573 X 10^-7 meters)

= 3.022 X 10^-19 Joules per photon

6573 A (1.0 X 10^-10 meter/1 A) = 6.573 X 10^-7 meters

Energy = Planck's constant * speed of light m/s/ wavelength in meters

E = (6.626 X 10^-34 J*s)(2.998 X 10^8 m/s)/(6.573 X 10^-7 meters)

= 3.022 X 10^-19 Joules per photon