Answer:
Each side of the garden should be 186.67 feet
Explanation:
We know that the biggest area of a rectangular prism is when it closer to a square, and we know that a square is a special kind of rectangle with all equal sides, so we want all the sides to be equal.
To do this we know that the Gardener has 560 feet of fencing and he is only going to fence 3 sides because the other side is bordered by a river.
So we have to divide the fencing by the sides to have equal sides:
560 feet / 3 sides = 186.67 feet per side.
So the garden will be a square with each side of 186.67 feet, and the area will be:
186.67 * 186.67 = 34,845.70 square feet.