Explanation:

Rectangular hyperbola is the shape of the average fixed cost (AFC) curve. The AFC curve is a rectangular hyperbola in the sense that all rectangles formed by AFC are of equal sizes. The typical shape of the average fixed cost (AFC) curve is generally downward-sloping. This is because as the level of output increases, the fixed costs are spread out over a larger number of units, resulting in lower average fixed costs per unit. In other words, as more and more units are produced, the fixed costs are spread over a greater quantity, leading to a decrease in average fixed costs per unit. This is why the AFC curve is downward-sloping. Hence option 4th is correct.