Considering all given compounds are in cation from -
(i) CH3 - \(\overset{+}{CH}\) - CH3
(ii) CH3 - \(\overset{+}{CH}\) - OCH3
(iii) CH3 - \(\overset{+}{CH}\) - \(\overset{O}{\overset{||}{C}}\) - CH3
Compound (1), cation stabilized by hyper conjugation with 6 hydrogen
in compound (2), cation stabilized by hyper conjugation as well as by loan pair electron of oxygen.
CH3 - \(\overset{+}{CH}\) - O - CH3 ↔ CH3 - CH = \(\overset{+}{O}\) - CH3
it means compound (2) also stablilized by Resonance but in compound (3), the cation stabilized by hyperconjation with 3 hydrogen but destabilized by strong electron with drawing group \(\Big(-\overset{O}{\overset{||}{C}}-CH_3\Big)\) and we also know that Resonance is powerful
Than Hyper conjugation because of that compound (2) is more stabilized than compound (1)
Hence order of stability
2 > 1 > 3