Draw cis-1-ethyl-4-isopropylcyclohexane in its lowest energy conformation.

The structure of cis-1-ethyl-4-isopropylcyclohexane is:

In disubstituted chair conformers of cyclohexane, in the cis-isomer the relation between substituents is axial-equatorial position. This means we have two possible chain conformers for this molecule:

The most stable conformer is the one with the most hindered group at the equatorial position because it causes a smaller steric effect. The most hindered group is isopropyl, meaning the second chain conformer has the lowest energy and is the most stable.