Answer:
$100
Explanation:
the marginal product per dollar spent on labor = 40 units / $20 = 2 units per dollar
the marginal product per dollar spent on capital = 60 units / $30 = 2 units per dollar
the marginal product per dollar spent on land = 2 = 200 / $X
$X = 200 / 2 = 100 ⇒ the cost per unit of land is $100
The marginal product per dollar spent on a factor of production (labor, capital or land) is MP(factor)/P(factor). It measures how many additional units of output can be obtained by spending $1 more in a factor of production.