The cis isomer is more stable because the eclipsed interactions between two ethyl groups stabilize the molecule.

The trans isomer is more stable because the eclipsed interactions between two ethyl groups stabilize the molecule.

The cis isomer is more stable because the eclipsed interactions between ethyl groups and hydrogens are more favorable than eclipsed interactions between ethyl groups

The trans isomer is more stable because the eclipsed interactions between ethyl groups and hydrogens are more favorable than eclipsed interactions between ethyl groups