Robinson has a labor endowment of 80 units of labor and a utility function u(x,y) = min { 2x, 5y }. The production of good x is x = 2(L_x)^0.5 and for y it is y = 4(L_y)^0.5. For Robinson, the optimal amount of good x to produce is _____ units.

A: 17.5 B: 15.5 C:12.1 D:10.1

dont answer by pen paper