Assume a fictitious world where there are four stocks:

General Electric (GE)

CitiGroup (C)

British Petroleum (BP)

FaceBook (FB)

The market is in equilibrium where CAPM assumptions hold (e.g. homogeneous expectations, efficient markets, zero transaction costs, etc.)Express the equilibrium condition for this universe of stocks in terms of each stock's return contribution and risk contribution.

Please give guidance!