Explanation: You are given one side of the aquarium which is 18 inches. The top and the bottom of the aquarium is 18 inches because that’s what the diagram gives us. So you can multiply 18 x 2=36. Now, to find the missing side length, subtract the perimeter (56 inches) by 36 and you get 20 inches. However, that’s not your final answer because you have to divide 20/2=10 inches. 10 inches is the missing side length for the left and right side lengths
