First, lets remenber a property of right triangles:
If we have the right triangle in this form:
The following is true:
[tex]h^2=m\times n[/tex]
In our question, Y=h , m=27 and n=3, with that we can solve our problem:
[tex]Y^2=27\times3\rightarrow Y^2=81\rightarrow Y=9[/tex]
So, Y=9
