A point at the end of a spinning helicopter blade has a centripetal
acceleration of 67.37 m/s2. If the velocity of the blade at this point is 16 m/s,
how long is the helicopter blade?
A. 3.8 m
B. 3.5 m
C. 3.1 m
D. 4.1 m

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