The IUPAC nomenclature of the compound above is 

Correct answer: 4-ethyloctane.

Explanation: Choose the longest continuous chain through the structure: going from the end of the propyl branch → central carbon → through the butyl side gives 8 carbons (octane). The remaining ethyl group is a substituent on the central carbon.

• Number the octane chain to give the substituent the lowest locant. Counting from the propyl end places the ethyl at C-4 (from the other end it would be C-5).
• Hence the IUPAC name is 4-ethyloctane, not 5-ethyloctane.
• Names with “propylheptane” use a shorter (7-carbon) parent chain and are therefore incorrect.