EXPLANATION
Let's see the facts:
The height of the triangle bisects it, so this is an Isosceles one.
The Area is 6.12 square feet.
By Isosceles Triangle Definition,

Isolating the base:
Multiplying both sides by 2:

Dividing both sides by the height:

Switching sides:

Replacing terms:

Answer: the length of the base is 3.6 feet.