Huanhuan's family wants to use one wall on the side of the house and build three walls to form a rectangular pigsty (as shown in the picture), with an entrance 1 m wide in the middle of one wall.

y = x( 12-2x)=-2x 2+ 12x，

(2) Let the length of the side perpendicular to the wall be xm,

Then x( 12-2x)= 16,

The solution is x 1 =2, x 2 = 4,

When x=2, 12-2x=8,

When x=4, 12-2x=4,

So the length of the side perpendicular to the wall is 2 meters or 4 meters;

(3) Let the length of the side perpendicular to the wall be ym,

Then y( 12-2y)=20,

Finishing, -2y 2+12y-20=0,

△= 144-4×(-2)×(-20)=- 16