4.1 Solutions included in the section.

4.2 Draw all conformers for 3-methylpentane by viewing along C2-C3 bond, and order them from the most stable to least stable.

4.3 Determine which is the more stable isomer, cis-1-ethyl-2-methylcyclohexane or trans-1-ethyl-2-methylcyclohexane?

The trans-isomer has the most stable conformer with both substituents are at equatorial positions, therefore trans-isomer is the more stable one.