Answer
$100^{\circ}$
Work Step by Step
This implies that the angle opposite to the angle $80^{\circ}$ is $80^{\circ}$ and the angle opposite to the angle $x^{\circ}$ is $x^{\circ}$. We know that the sum of the angles is $360^{\circ}$ .
Therefore, we write the equation and then solve for $x$ as: $80^{\circ}+x^{\circ}+80^{\circ}+x^{\circ}=360^{\circ}$
or, $160^{\circ}+2x=360^{\circ}$
or, $2x=200^{\circ} \implies x=100^{\circ}$
