Wavelength = velocity/frequency of time .....(1)

Here we know that

frequency =1/T

By putting value in equation (1) or formula

340×0.01=3.4 ans

I am sorry but am not able to explain derivation  because it needs diagram and without you can't understand it but if you wanted tell me i will try

By the way you can use career 360 sites question papers

I hope it will help you

Thank you