Ta có:

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

Mà $\widehat{xOy}+\widehat{{x}'O{y}'}={{216}^{0}}$ nên:

$\widehat{xOy}=\widehat{{x}'O{y}'}={{216}^{0}}:2$

$\Rightarrow \widehat{xOy}={{108}^{0}}$

Mặt khác ta có:

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

$\Rightarrow {{108}^{0}}+\widehat{xO{y}'}={{180}^{0}}$

$\Rightarrow {{\widehat{xOy}}^{\prime }}={{180}^{0}}-{{108}^{0}}$

$\Rightarrow \widehat{xO{y}'}={{72}^{0}}$

Đáp án: B