Answer: 40°
Explanation:
<3 is congruent to <17
This means that <17 = 140°
<17 and <18 are supplementary angles, meaning <17 + <18 = 180°.
You can substitute <17 = 140° into this equation, making the equation 140° + <18 -= 180°.
If you subtract 140 from both sides, you are left with <18 = 40°.