Question

find the wavelength step wise ​

Answer 1

By convention, a wavelength can never be negative. Neither can a frequency.

so I am sorry to say that your question or your solving method is a bit incorrect... because by stepwise method the wavelength turns out to be negative ❎ which is not possible. anyways here is the answer to your question. please check the sign convention of your question ... hope u have a great day ☀