I don't understand when to use the formule with the constant k, and when to use the formula without it. In the exercise that i sent here, they use the formule with a constant but I don't get why.

Can someone help me out please?
Thanks.

.) the observation by semmelweis that more mothers died of childbed fever when their doctors also worked in the morgue

distance = 150m

displ = root (50 ^2 + 100^2)

root(2500+10000)

root 125000

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