3C. Long-Run Labor Demand
Hire inputs until increasing output costs same if by more labor or more capital.
Cost of one more unit of output = w/MPL if labor used = c/MPK if capital used (c=user cost of K)
So w/MPL = c/MPK or w/c = MPL/MPK
e.g. wskilled/wunskilled = MPskilled/MPunskilled