How many units of labor should a firm hire in order to maximize profits?

Question

Capital is fixed at 16 units. The firm can sell its output at a price of $100 per unit and can hire labor at $25 per unit.

Answer 1

Equilibrium is at point where MR=MC or MRPL=MFC

MRPL=MPL*MR=MPL*P=MPL*100

MFC=$25 = W

MC=W/MPL=$25/MPL

MR=P=$100

case [1]: MRPL=MFC → 100MPL=25

case [2]: MC=MR → 25/MPL=100

Thus you should provide production function to solve right - because it is required to know marginal worker productivity.