A cylindrical water tank has a radius of 3 feet and a height of 10 feet. It is partially filled with water up to a height of 6 feet. If the water is to be transferred to smaller cylindrical containers each with a radius of 1 foot and height of 2 feet, how many such containers can be completely filled with the water from the tank? Let's think step by step and output the final answer within \boxed{}.
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