A circular grass plot with a diameter of 12 feet is intersected by a straight gravel path that is 3 feet wide. One edge of the path passes through the center of the plot. Calculate the number of square feet in the remaining grass area. The original answer is in the form $k\pi - m\sqrt{n}$, please provide the value of k + m + n.

Let's think step by step and output the final answer within \boxed{}.
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