A rectangular aquarium has dimensions of 24 inches in length, 12 inches in width, and 18 inches in height. It is filled with water up to a height of 15 inches. If a solid rectangular object with dimensions 10 inches long, 6 inches wide, and 5 inches high is fully submerged in the aquarium, what will be the new water level in the aquarium? Let's think step by step and output the final answer within \boxed{}.
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