A firm's output (Y) depends on how much capital (K) it has, according to the equation: Y = 20K - K2. The real interest rate is 6% per year, the depreciation rate of capital is 14% per year and the price of a unit of capital is $80, and each unit of output sells for $1. The real price of capital is not expected to change. Complete the Table below by calculating output and the marginal product of capital (MPK) for capital levels 1 - 6.

Capital Output Marginal Product of Capital (MPK) 0 0 ---- 1 2 3 4 5 6

At a real interest of 6%, how many units of capital does the firm desire? Briefly explain your answer.