Answer:
λ=589nm
Step-by-step explanation:
The wavelength of the sodium light can be calculated using the next equation:
where Λ: is the distance between the adjacent bright regions, λ: is the wavelength of the sodium light, L: is the distance between slits and screen, and D: is the distance between slits.

Therefore, the λ of the sodium light is 589 nm.
I hope it helps you!