Since the sum of the internal angles of a triangle is 180 degrees then you have the following
[tex]\begin{gathered} 90+(6x+y)+(4x+2y)=180 \\ 90\text{ because it is a right triangle} \end{gathered}[/tex]
Since angle Y is right, that is, it measures 90 degrees, then its supplementary angle also measures 90 degrees, because 90 + 90 = 180.
Now
