Ta có:

$\widehat{xOy}=\widehat{x'Oy'}$ ( Do hai góc đối đỉnh )

Mà $\widehat{xOy}+\widehat{x'Oy'}={{248}^{0}}$ nên:

$\widehat{xOy}=\widehat{x'Oy'}={{248}^{0}}:2$

$\Rightarrow \widehat{xOy}={{124}^{0}}$

Mặt khác ta có:

$\widehat{xOy}+\widehat{xOy'}={{180}^{0}}$

$\Rightarrow 124+\widehat{xOy'}={{180}^{0}}$

$\Rightarrow \widehat{xOy}'={{180}^{0}}-{{124}^{0}}$

$\Rightarrow \widehat{xOy'}={{56}^{0}}$

Đáp án: B