Answer:
[tex]m\angle Y=30^{\circ}[/tex]
Step-by-step explanation:
In any right triangle, the cosine of an angle is equal to its adjacent side divided by the hypotenuse, or longest side, of the triangle.
Therefore, we have:
[tex]\cos Y=\frac{42\sqrt{3}}{84},\\Y=\arccos(\frac{42\sqrt{3}}{84})=\boxed{30^{\circ}}[/tex]
