Answer:
x = 11
Step-by-step explanation:
Properties of a square,
1). Diagonal of a square bisect the opposite angles.
2). All interior angles of a square measure 90°.
From these properties,
m∠PQR = 90°
Since, diagonal QS bisects angle PQR,
m∠PQS = m∠RQS = 45°
(6x - 21)° = 45°
6x = 45 + 21
6x = 66
x = 11
