Answer:
 36 ft
Step-by-step explanation:
Let L represent the length of Louis's basement. The area is the product of length and width, so is ...
 A = L(L/3)
 432 = L²/3 . . . . . fill in area value
 1296 = L² . . . . . . multiply by 3
 36 = L . . . . . . . . . take the square root
The length of Louis's basement is 36 feet.