A triangle is 180°, so the 3 angles should add up to 180°.
To find m∠R, you can do this:
m∠S + m∠R + m∠T = 180°
56° + m∠R + 30° = 180°
m∠R + 86° = 180° Subtract 56 and 30 on both sides
m∠R = 94°
