Answer:
the least cost rule
Explanation:
Imperfect markets are those where all the conditions for perfect markets don't exist. In perfect markets, the profit maximizing rule for hiring labor is that you will continue to add labor until marginal revenue product = marginal cost of labor. The same applies for capital or land which are the other factors of production.
But on imperfect markets, this is not that clear, the equation in this case would be:
least cost rule ⇒ marginal product of labor / marginal cost of labor = marginal product of capital / marginal cost of capital
