Answer:
Option 3rd is correct
square feet
Explanation:
Perimeter(P) and Area(A) of equilateral triangle is given by:

....[1]
where, a is the side of the equilateral triangle.
As per the statement:
The perimeter of an equilateral triangle is 12 feet
By definition of perimeter:


Divide both sides by 3 we have;

or
a = 4 ft
Substitute in [1] we have;

Therefore, the area of the equilateral triangle is,
square feet