Points P, Q and S are collinear what is m

In triangle abc, the length of side ab is 12 cm, the length of side bc is 5 cm, and the length of side ca is 9 cm. find the measure of angle a using the law of cosines.

1) what is the measure of the exterior angle, ∠uvw ? 2) in triangle man, what is the measure of the exterior angle at n (in degrees)?

Which number completes the inequality? 2/3 < _ < 7/9