Explanation

To determine when margin calls occur, we need to track the cumulative gains/losses from the initial position. Since the question doesn't specify initial margin requirements, we'll analyze the pattern of losses:

• June 29: Starting point (0 gain)
• June 30: +700 (cumulative: +700)
• July 1: -6,600 (cumulative: -5,900) - Large loss, likely margin call
• July 2: -3,100 (cumulative: -9,000) - Continued losses, margin call
• July 6: +2,800 (cumulative: -6,200) - Recovery
• July 7: -3,000 (cumulative: -9,200) - Significant loss again, margin call
• July 8: -1,000 (cumulative: -10,200) - Loss but smaller

The pattern shows margin calls would likely occur on days with substantial losses that push the account below maintenance margin levels: July 1, July 2, and July 7.