Volume of a cube
We know that all the sides of a cube have the same measures:
and its volume is given by
side * side * side = side³
Then, in this case
side = 9 in
↓
volume = (9 in)³
↓ since 9³ = 27
volume = 27 in³
Then, we will need 27 in³ of soil to fill the planter.
Answer: 27 in³