An experiment because you need to change variables to get different outcomes and that is in an experiment
Volume is 2.3×2.4×20=110.4 cm^3
there is given an object mass, so maybe you need a density too?
density = mass / volume = 17.5/110.4=0.1581 g/cm^3
The wavelength is the distance between one crest/trough to another crest/trough. On the image, it's basically the length between each peak of the wave. You can see that the distance between peaks in wave A are much shorter than the distance between the peaks in wave B.
Thus, wave B has the longer wavelength.