The formula for finding the area of a triangle is A = 1/2 b x h
Since we are given the area and the height, we can easily substitute these values into the equation then solve for the unknown width (base).
A = 1/2 b x h
6 = 1/2 b x 4
12 = b x 4
12/4 = b
b = 3 ft
Check the answer by plugging back into the formula
6 = 1/2 (3 x 4)
6 = 1/2 * 12
6 = 6 True statement so it checks!