Find the arc length of the shaded sector please I don't want to fail

Asap 25 pts + brainlest to right/best answer

The swimming pool is open when the high temperature is higher than 20∘c. lainey tried to swim on monday and thursday (which was 33 days later). the pool was open on monday, but it was closed on thursday. the high temperature was 30 ∘c on monday, but decreased at a constant rate in the next 33 days. write an inequality to determine the rate of temperature decrease in degrees celsius per day, d, from monday to thursday.

What is the missing reason in the proof? segment addition congruent segments theorem transitive property of equality subtraction property of equality?