We will solve this problem by unitary method which states:
"The unitary method is a technique which is used for solving a problem by finding the value of a single unit, i.e., 1, (by dividing) and then finding the necessary value by multiplying the single unit value."
Numbers of plotted plants watered by
of water in a bucket = 1 plant.
Number of plotted plants watered by the amount of water in 1 bucket =

=

= 4 plants.
Number of plotted plants watered by the amount of water in 3 buckets =

= 12 plants.