Because AR = AQ, you have an isosceles triangle with triangle RAQ. This also means ∠ARQ = ∠AQR.
You're also told that RT = QS, so this gives you SAS to show triangle ART = triangle AQS.
side: AR = AQ
angle: ∠ART = ∠AQS
side: TR = QS
Knowing that the two triangles are congruent gives you that the two top angles are also congruent.