Help me with following question.

The answer for this question is 50k N.m

cube of any positive integer is of the form 9m,9m+1 or 9m+8. In this question, why do we take a=3q, a=3q+1 and a=3q+2. why cant we take a=2q and a=2q+1. or a=5q, 5q+1, 5q+2, 5q+3 and 5q+4. why do we specifically use a=3q and 3q+1 if a is any positive integer and can be represented in other ways?

absorption lines are where light has been absorbed by the atom thus you see a dip in the spectrum whereas.

emission spectra have spikes in the spectra due to atoms releasing photons at those wavelengths.

explanation:

0.11 m/s and 0.28 m/s should be correct