Final answer:
The measure of the third angle is 109°.
Step-by-step explanation:
The sum of all three angles in a triangle is always 180°.
To find the measure of the third angle, we can subtract the sum of the given angles from 180°:
180° - (54° + 17°) = 180° - 71° = 109°
Therefore, the measure of the third angle is 109°.
Learn more about Triangle angles