Whats his mistake and the correct awnser

Answer:
θ ≈ 35.7°
Step-by-step explanation:
His mistake was in using the wrong trig. ratio
Instead of using cosine he should have used the sine ratio
sinθ = [tex]\frac{opposite}{hypotenuse}[/tex] = [tex]\frac{7}{12}[/tex] , then
θ = [tex]sin^{-1}[/tex] ([tex]\frac{7}{12}[/tex] ) ≈ 35.7° ( to the nearest tenth )