Answer: is c (70 degrees) I hope it helps anyone.
Step-by-step explanation:
RS is a tangent ⇒ ∠OSR = 90°
RT is a tangent ⇒ ∠OTR = 90°
OSRT is a quadrilateral, so has an angle sum of 360°
⇒ ∠OSR + ∠SRT + ∠OTR + ∠SOT = 360°
⇒ 90° + 40° + 90° + ∠SOT = 360°
⇒ 220° + ∠SOT = 360°
⇒ ∠SOT = 140°
Now use the Angle at the Center Theorem
∠SUT = ½ × ∠SOT = ½ × 140° = 70°