In order to get the amount of water we would like to have in cubic feet, we must first subtract 0.25 ft (the distance from the top the waterline must be) from the height
1.5-0.25=1.25
Next we multiply the length, width, and new height in order to find the volume
2*1*1.25=2.5ft^3
We divide this by the volume of water the bucket can hold
2.5/1.25=2
Thus, we need 2 buckets of water in order to fill the tank
