The angles are supplementary, so their sum is \(180^\circ\). The equation is:
\[
(5x + 15) + (4x - 6) = 180
\]
Simplification yields:
\[
9x + 9 = 180 \quad \Rightarrow \quad 9x = 171 \quad \Rightarrow \quad x = 19
\]
Substitute \(x = 19\) to find the angles:
\[
5x + 15 = 5 \cdot 19 + 15 = 100^\circ, \quad 4x - 6 = 4 \cdot 19 - 6 = 80^\circ
\]
The answer is \(100^\circ, 80^\circ\).