Suppose the returns on all well-diversified portfolios are determined by the following two factor model

Consider the following statement: if any two well-diversified portfolios, A and B, have the same betas on each factor, they must have the same expected returns.

Use an absence of arbitrage argument (similar to the one used in class) to prove this statement. Please make sure you write down and carefully explain each step of the proof.

ASAP PLEASE ...ASAP