Since triangles \( \triangle XYZ \) and \( \triangle RST \) are similar, the sum of the angles in each triangle must equal \( 180^\circ \).
First, calculate the measure of angle \( Y \) in triangle \( XYZ \):
\[ m\angle Y = 180^\circ - m\angle X - m\angle Z \]
However, we don't have the measure of angle \( Z \) provided. We can solve for angle \( T \) in triangle \( RST \) using the measure of angle \( S \).
Now, in triangle \( RST \):
\[ m\angle R + m\angle S + m\angle T = 180^\circ \]
Given \( m\angle S = 79^\circ \), we need to determine \( m\angle R \) using the corresponding angle in triangle \( XYZ \) due to the similarity of the triangles.
Since \( \triangle XYZ \sim \triangle RST \), the angles \( X \) and \( R \) are corresponding angles. Therefore, we can find \( m\angle R \):
\[ m\angle R = m\angle X = 50^\circ \]
Now we can substitute \( m\angle R \) and \( m\angle S \) back into the equation for triangle \( RST \):
\[ 50^\circ + 79^\circ + m\angle T = 180^\circ \]
\[ 129^\circ + m\angle T = 180^\circ \]
Now, solving for \( m\angle T \):
\[ m\angle T = 180^\circ - 129^\circ = 51^\circ \]
Thus, the measure of angle \( T \) is:
\[ \boxed{51^\circ} \]