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a = 1 ; c = 4 ; V = 6
V = a * b * c --> b = V / (a * c) = 6 / (1 * 4) = 6/4 = 3/2 = 1.5
O = 2 * (a * b + a * c + b * c) = 2 * (1 * 1.5 + 1 * 4 + 1.5 * 4) = 2 * (1.5 + 4 + 6) = 2 * 11.5 = 23