A 60-Watt bulb illuminates a surface a distance d away with an illuminance of 2400 lux. What would be the illuminance on a surface a distance 2d away (i. e. twice as far away) when illuminated by a 30-Watt bulb?

a skateboard rolling across the street - apex

you'd use the equation that establishes a relationship between  energy  and  wavelength, which looks like this

e=h⋅cλ, where

λ  - the wavelength of the photon; c  - the speed of light, usually given as  3⋅108m/s; h  -  planck's constant, equal to  6.626⋅10−34j s

plug the value you were given for the energy of the photon in the above equation to get the wavelength

e=h⋅cλ⇒λ=h⋅ce

λ=6.626⋅10−34js⋅3⋅108ms−1.257⋅10−24j=1.581⋅10−1m