Answer:
Hey there!
First, we want to find the side length of the large triangle.
1/2bh=y cm^2
bh=2y cm^2
Since b and h are the same here, we have b^2= 2y, 
. 
And we have FC=
. 
Area of shaded triangle: 
.
This is equal to: 
, or y/4.
Let me know if this helps :)