Question 1103623
A=(1/2)bh
The side is s.
The altitude divides the equilateral triangle into 2 30-60-90 triangles, because the altitude is a bisector of one of the 60 degree angles.

The sine of 30 degrees is the opposite side (or half s) over the hypotenuse, or s.
The Pythagorean theorem has the hypotenuse squared (s^2)= opposite side squared (s/2)^2 plus the adjacent side, the altitude, which is (s/2) sqrt (3) or h.
Therefore h=(s/2) sqrt(3)
The area is (1/2)s*(s/2) sqrt (3) or (s^2/4)sqrt(3) ft^2.