The are two angles given on the diagram, an interior angle at S and an exterior angle at T.
The Exerior Angle Theorem connects the measure of an exterior angle of a triangle to the remote interior angles of the same triangle.
The sum of the measures of the
interior angles atSandR
is the measure of the exterior angle atT.
We are given the measure of the exterior angle at T and the interior angle at S, so we can use this relationship to find m∠ R.
