Answer:
V = (18 in²)x, where x is the unknown third dimension
Step-by-step explanation:
What was the third dimension? I'll call it x and you can assign a value to x:
Volume of box = V = (length)(width)(height)
Here, we have V = (6 in)(3 in)( x ), so the formula for the volume is
V = (18 in²)x
