∠pqr=∠pqs+∠sqt+∠tqr=∠pqt-∠sqt+∠sqt+∠sqr-∠sqt
=∠pqt-∠sqt+∠sqr
=90°+90°-∠sqt
=128°
所以∠sqt=180°-128°=52°
sqt的度数为52度