6. On January 1, 2020, Syscon Company granted a performance-based stock option plan to 20 executives. It allowed each of them to buy a maximum of 4,000 shares of the company's $5 par option common stock at an exercise price of $15 a share. On the grant date, the fair value per option was $9. The shares will be awarded based on the increase in sales over a four-year service and vesting period as follows: Sales Increase On Dec. 31, 2020, the company estimated sales would increase by 6.5% during the service period and that 18 employees would get vested. On Dec. 31, 2021, the company estimated that 16 employees would get vested, and sales would still increase by 6.5%. On Dec. 31,2022 , the company maintains the same estimates for the number of employees to get vested and the percentage of sales increase with those made on Dec. 31, 2021. At the end of the four-year period (Dec. 31, 2023), options actual vested for the remaining 17 executives and sales actually increased only by 4%. On this date, the fair value per option changed to $8.50. Required (20 points): Prepare the journal entries to reflect the events affecting this plan for the four-year service period