A firm uses only input A and input B to create an output. Suppose that initially the firm uses 10 units of input A and produces 5 units of output. When the firm increases its use of input A to 11 units, it produces 8 units of output. In addition, when the firm increases its use of input A again to 12 units, it produces 12 units of output. Assume all the amount of input B used remain constant.

How does this relate to the law of diminishing marginal returns?