Answer:
b = 60
Explanation:
We know: The sum of measures of angles in a triangle is equal to 180°.
Therefore we have the equation:
b° + 80° + 40° = 180° combine like terms
b° + 120° = 180° subtract 120° from both sides
b° + 120° - 120° = 180° - 120°
b° = 60°