The rental price paid to each owner of capital is equal to what?

The rental price paid to each owner of capital is determined by the marginal product of capital (MPK). In macroeconomic theory, the MPK reflects the additional output that can be produced with one more unit of capital, holding all other inputs constant. When firms decide to hire or rent capital, they will do so up to the point where the value of the additional output generated by that capital equals its rental price.

Thus, the rental price aligns with the MPK because it represents the economic return to capital. If the rental price were lower than the MPK, firms would have an incentive to rent more capital, as the additional output would justify a higher price. Conversely, if the rental price exceeds the MPK, firms would reduce their demand for capital since the cost would outweigh the returns. Therefore, the equilibrium rental price of capital is effectively linked to the marginal productivity of the input, confirming that the correct answer is indeed the marginal product of capital.