What is the correct order of decreasing stability of the following cations ?

$\text{ I. }{\mathrm{CH}}_3-\stackrel{\oplus }{\mathrm{C}}\mathrm{H}-{\mathrm{CH}}_3$

$\text{ II. }{\mathrm{CH}}_3-\stackrel{\oplus }{\mathrm{C}}\mathrm{H}-{\mathrm{OCH}}_3$

$\text{ III. }{\mathrm{CH}}_3-\stackrel{\oplus }{\mathrm{C}}\mathrm{H}-{\mathrm{CH}}_2-{\mathrm{OCH}}_3$

$\text{ ।. }{\mathrm{CH}}_3-\stackrel{\oplus }{\mathrm{C}}\mathrm{H}-{\mathrm{CH}}_3$ Weak + I-effect of the two methyl groups stabilises carboncation ( I)

II. ${\mathrm{CH}}_3-\stackrel{\oplus }{\mathrm{C}}\mathrm{H}-{\mathrm{OCH}}_3$ Strong + R-effect of $-{\mathrm{OCH}}_3$  group stabilises carboncation (II)

$\text{ III. }{\mathrm{CH}}_3-\stackrel{\oplus }{\mathrm{C}}\mathrm{H}-{\mathrm{CH}}_2-{\mathrm{OCH}}_3$ -I-effect of $-{\mathrm{OCH}}_3$ group destabilises carboncation (III)

Hence, the stability of carbocation decreases in the following order II > I > III.