Answer:
57°
Explanation:
You can notice that by putting ∠3 and ∠TKL together you have a flat angle.
A flat angle has 180 degrees.
so, you can say that m∠3 and m∠TKL add 180 degrees, then they are supplementary angles.
Remember: Two angles are supplementary if they add 180 degrees.
Then, as you know m∠3=123°:
m∠3 + m∠TKL=180°
123 + m∠TKL=180°
m∠TKL=180° - 123°
m∠TKL=57°