The correct answer is C) 6.51 feet. To calculate the reduction in GM (metacentric height) due to free surface, we can use the formula: Reduction in GM = (I/V) * W, where I is the moment of inertia of the free surface, V is the displacement volume, and W is the weight of the free surface. Given: - Vessel displacement = 747 tons - Vessel dimensions = 136'L x 34'B - Water on the after deck = 56'L x 34'B, weight = 58.6 tons Calculating the moment of inertia (I) of the free surface: I = (56 * 34^3) / 12 = 54,912 ft^4 Calculating the displacement volume (V): V = 747 tons / 64 (density of seawater) = 11,672.5 ft^3 Plugging these values into the formula: Reduction in GM = (54,912 / 11,672.5) * 58.6 = 6.51 feet Therefore, the correct answer is C) 6.51 feet.