Answer:
UK = 75°
Explanation:
the measure of the chord- chord angle TRS is half the sum of the measures of the arcs intercepted by the angle and its vertical angle.
∠ TRS =
(TS + UK) , that is
87° =
(99 + UK) ← multiply both sides by 2 to clear the fraction
174° = 99° + UK ( subtract 99° from both sides )
75° = UK