A certain countries production is described by the Cobb-Douglas function f(x, y) = 90x1/3y2/3 where x units of labor and y units of capital are used. (10 points) a. What are the marginal productivity of labor and the marginal productivity of capital when the amounts expended on labor are 155 units and 20 units, respectively? b. Should the government encourage capital investment rather than increased expenditure on labor at this time to increase the country's productivity