These `SN^2` reaction invert configuration.
(a) `(S)-CH_3CH(OMe)CH_2CH_3`
(b) `(R)-CH_3CH(OMe)CH_2CH_3`
(c)
The priority order changes. In `(A)`, the highest priority is `Br` and in `(B)`, the highest priority is `COOEt`. So the absolute configuration is same.