In a cyclic quadrilateral (one inscribed in a circle), the opposite angles are supplementary. This means that the sum of the two opposite angles equals 180°.
Given:
- One angle is 108°
- The angle opposite to it (let's call it x) must satisfy the relation:
\[ 108° + x = 180° \]
Now, we can solve for x:
\[ x = 180° - 108° = 72° \]
Thus, the value of \( x \) is:
\[ \boxed{72} \]