What is the outer boundary of the cell that is semi-permeable?

Answer is Plasma membrane or cell membrane.

The plasma membrane or cell membrane is a delicate, two-layered structure made of lipids and proteins (lipoprotein) present in all living cells. The lipids are largely specialized lipids called phospholipids. It separates the cell interior from the outside environment. It is a semipermeable membrane, it means it controls the move met of molecules across the membrane. It allows only certain molecules can pass through.

the correct answer would be 6 feet.