Question

Calculate the wavelength of a photon having energy of 1.257 X 10-24 joules. (Planck’s constant is 6.626 x 10-34 joule seconds; the speed of light is 2.998 x 108 m/s)

Answer 1

For this equation you need to use the equation $E=h\frac{c}{λ}$ 

E is your Energy, h is Planck's constant, c is the speed of light and λ is wavelength

First re-arrange the equation to get λ by itself since that's what we are calculating

λ = h (c/E) plug in numbers
λ = 6.626 x10^-34Js [(2.998 x 10^8m/s)/1.257 x10^-24J)] evaluate
λ = 6.626 x10^-34 (2.385 x10^32)
λ ≈ 0.158 m