see the picture with letters attached to better understand the problem
we know that
in the right triangle ABC
AB=BC----------> by angle 45°
AC²=AB²+BC²-----> AC²=(√2)²+(√2)²----> AC²=4-----> AC=2
in the right triangle ACD
tan 60°=y/AC--------> y=AC*tan 60°-----> y=4*tan 60°----> y=4√3
the answer is
y=4√3
