Supplementary angles are two angles that add up to \(180^\circ\). If \(x^\circ = 125^\circ\), we can find \(y^\circ\) using the relationship:
\[ x + y = 180 \]
Substituting \(x = 125\):
\[ 125 + y = 180 \]
To isolate \(y\), subtract \(125\) from both sides:
\[ y = 180 - 125 \] \[ y = 55 \]
Therefore, the value of \(y^\circ\) is \(55^\circ\).
The correct answer is:
D. 55°