What is the measure of ∠R?

Answer:
∠ R ≈ 36.9°
Step-by-step explanation:
Using the cosine ratio in the right triangle
cos R = [tex]\frac{adjacent}{hypotenuse}[/tex] = [tex]\frac{RT}{RS}[/tex] = [tex]\frac{8}{10}[/tex] , thus
∠ R = [tex]cos^{-1}[/tex] ([tex]\frac{8}{10}[/tex] ) ≈ 36.9° ( to 1 dec. place )