please EXPLAIN please can you help me with excell formulaa thank u so much in advance

Based on the following information, calculate the expected return and standard deviation for PSE&G and Potomac Electric Power Company (PEPCO) stock. (75 POINTS) State of Economy Recession Normal Boom Probability of State of Economy 20.0% 70.0% 10.0% Rate of Return if State Occurs PSE&G PEPCO -5.3% -7.7% 10.8% 14.3% 26.0% 30.5%