Lines $r$ and $s$ are parallel. A transversal line $t$ intersects $r$ and $s$. The angle formed by line $r$ and line $t$ in the upper-left interior position is $115^{\circ }$. A second transversal, line $u$, intersects line $s$ and line $t$, forming a triangle. If the angle formed by line $s$ and line $u$ on the left side of line $u$ is $60^{\circ }$, what is the measure, in degrees, of the third angle in the triangle formed by lines $s$, $t$, and $u$?