Let's put more details in the given figure to understand the problem:
From the figure above, we have three (3) named angles: ∠x, ∠y & ∠z
Using the principle of trigonometric functions, we get:
[tex]\text{ Sin y = Cos x}[/tex]
With the given AC = 9 and BC = 12, we can find ∠x using the Tangent Function. We get,
[tex]\text{ Tan x = }\frac{\text{ 9}}{\text{ 12}}[/tex][tex]\text{ x = }\tan ^{-1}\text{ (}\frac{9}{12})[/tex]
[tex]\text{ x = 36.8698976}^{\circ}\text{ }\approx36.87^{\circ}[/tex]
Let's now determine what is Cos x.
[tex]\text{ Cos x = Cos (36.87}^{\circ})[/tex]
[tex]\text{ Cos x = 0.7999989 }\approx\text{ 0.8}[/tex]
Since Cos x = Sin y, therefore, we can conclude that Sin y = 0.8
ANSWER: Letter B - 0.8
