In the previous post, the solution noted that the multiplets at 1.2 and 3.5 ppm were related to a single compound (labeled B on the 1H NMR spectrum below). This post will attempt to clarify this reasoning.

The relative integrals for the multiplets at 1.2 and 3.5 ppm are 1.20 and 0.81, respectively.

The ratio of the integrals = 1.20:0.81 or 1.48:1 or 2.96:2 or 4.44:3

The ratio 2.96:2 closely resembles a 3:2 ratio, or potentially a CH3:CH2. Furthermore, the coupling patterns t and q support a methyl group adjacent a methylene group.