Answer: The tank which has 3 m side.
Step-by-step explanation: A cube is a form that has equal sides. To calculate the volume of it, multiply all three sides:
V = length*width*height
Since they are all the same, volume will be:
V = s³
One tank has a 3 m side, so its volume is:
V = 3³
V = 27 m³
The other has half of the first one side, then s =
and volume will be:
V =

V =
m³
As you can see, the volume of the second tank is
smaller than the first one. Therefore, the tank which has 3 m side can store more water than the tank with side measuring half of the first.