Does anyone know this answer I don’t get it

Answer:
∠ XYZ ≈ 66.4°
Step-by-step explanation:
Using the cosine ratio in the right triangle
cosY = [tex]\frac{adjacent}{hypotenuse}[/tex] = [tex]\frac{XY}{YZ}[/tex] = [tex]\frac{6}{15}[/tex] , then
∠ Y = [tex]cos^{-1}[/tex] ([tex]\frac{6}{15}[/tex] ) ≈ 66.4° ( to 1 dec. place )