A mirror has an object located on its principal axis 33.5 cm from the mirror's surface. A virtual image is formed 41.4 cm behind the mirror. What is the mirror's focal length?
a.-263.34 cm
.b. 64.81 cm
C. 175.56 cm
d. -0.38 cm
e. 9.26 cm

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