Answer:
m∠3 = 38.9°
Step-by-step explanation:
If all three angles of a triangle adds up to 180° (Triangle Sum Theorem), it is a right angle (meaning that one of the angle measures is 90°), and m∠1 = 51.1°, then:
m∠1 + m∠2 + m∠3 = 180° (Triangle Sum Theorem)
51.1° + 90° + m∠3 = 180° (Substitution Property of Equality)
141.1° + m∠3 = 180° (Addition Property of Equality)
m∠3 = 38.9° (Subtraction Property of Equality)
