To find the volume of a rectangular prism, we must multiply the length * width * height.
In this case,
Volume = 3 ft * 2 ft * 1 ft
= 6 ft^3
Because this tank is 2/3 full with water, to find out how much water is in the tank, we must multiply 2/3 by the total volume of the tank (6 ft^3).
2/3 * 6 ft^3 = 4 ft^3
This means that there are 4 cubic feet of water in the tank.
Hope this helps!