Hello!
∠S measures 75° because the angle opposite of it measures 75°. An opposite angle always measures the same as the other angle.
[tex]\angle s = 75 \°[/tex]
∠T = 180 - 75 because the angle on the other side measures 75° and the angle is a straight angle, which measures 180°
180 - 75 = 105
[tex]\angle t = 105 \°[/tex]
