Similarity of two triangle
Similarity: two triangle are similar (they have the same shape but generally different size) if and only if the have the same angles.
In this case, we have that:
ΔTSU ≅ ΔUVW
because they have the same angles
We know this because:
Vertical angles: when two lines are crossed, the opposite angles formed are equal. These angles are called vertical angles.
Since TS and VW are parallel
Alternate interior angles: when two parallel lines are crossed by a transversal, there are couples of angles formed that are equal. Those are called alternate interior angles.
Answer
ΔTSU ≅ ΔUVW
by vertical angles and alternate interior angles
