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1. If [[2, 3, -3], [7, 4, -1]] * [[3], [6]] = [[13]], then find x and y.
2. Find the rank of the matrix: [[3, -1, -2], [2, 4, 1], [-6, -3, 2]].
3. The total cost function for producing x units of a product is TC = 60 - 12x + 2x^2. Find the average cost function and the level of output at which it is minimized.