In a triangle, the sum of the measures of the angles is always 180°.
Given the two angles:
- First angle = 25°
- Second angle = 55°
To find the third angle, you can use the formula:
\[ \text{Third angle} = 180° - (\text{First angle} + \text{Second angle}) \]
Substituting the known values:
\[ \text{Third angle} = 180° - (25° + 55°) \] \[ \text{Third angle} = 180° - 80° \] \[ \text{Third angle} = 100° \]
Therefore, the measure of the third angle is 100°.
The correct answer is B. 100°.