Let H be the height of the triangle. We don't know what the value of H is, but we know that the base is 3*H, or three times the height.
Multiply the height and base, then divide by 2, to get the area 6. Solve for H
(base)*(height)/2 = area
(3*H)*(H)/2 = 6
(3H^2)/2 = 6
3H^2 = 6*2
3H^2 = 12
H^2 = 12/3
H^2 = 4
H = sqrt(4)
H = 2
The height is H = 2 so the base is 3*H = 3*2 = 6
Answer is choice A) 6 ft