2. Two goods, Food (f) and Cloth (c), are produced. According to the specific factors model, there are three production factors: Labour (L), Capital (K) and Land (T). The production function is concave and the marginal product of each production factor diminishes as the output increases. The prices of Food and Cloth are and , respectively. The quantities of Food and Cloth are and . The wage of the labour is w .
(3) Please discuss why the slope of PPF equals to ,where is the marginal product of labour in Food and MPLc is the marginal product of labour in Cloth.