trans-1,3-Dimethylcyclohexane
One methyl group (green) is equatorial and one methyl group (red) is axial in this conformation of the trans-stereoisomer. The ring-flip conformation interchanges the axial and equatorial methyl groups. This compound is less stable than the cis-stereoisomer, which has a conformation with both methyl groups equatorial (see Practice Problem 6.4).
In contrast, in the case of 1,2-dimethylcyclohexane, it is the trans-stereoisomer that is more stable because it has the conformation with both methyl groups equatorial.