I can't answer this question if the structural formula is not given. However, I found a similar problem in terms of wording. Taking this problem to be solved, let's take a look at the structural formula as shown in the second picture. First, you must know the parent chain, which is the longest chain. This is a trial-and-error process. The longest chain which has a branching group that is nearest to the head is the correct numbering. In this case, the longest chain has 8 carbon atoms. Thus, the base of the name if octane. Because a 3-carbon chain is branching from the 4th carbon, the IUPAC name of the compound shown is: 4-propyloctane.
