Question

How do I solve for Y?

Answer 1

Start with the small triangle on the right:

   35 + 96 + x = 180

   x = 49

Ah, you already have that.  Nice!

Now move to the biggest triangle:

   x + 77 + (35+y) = 180

but x = 49, so

   49 + 77 + 35+y = 180

   y = 19