The Productivity of a Certain Country Is P(x, Y) = $x ^ { 1 / 4 }$

Multiple Choice

The productivity of a certain country is P(x, y) = 1600 $x ^ { 1 / 4 }$ $y ^ { 3 / 4 }$ units, where x and y are the amounts of labor and capital utilized. What is the marginal productivity of capital when x = 16 and y = 625?

A) 1600
B) 5000
C) 480
D) 2500
E) none of these