13. On January 1, 2016, Robertson Company created a fixed compensatory stock option plan for employees to acquire 18,000 shares of $3 par common stock for $22 a share. The options vest after four years of employment, and therefore, they cannot be exercised until January 1, 2020. On the grant date, the fair value of the options was $5 per option. All options were exercised on June 30, 2020. Robertson Company accounts for this plan using the fair value method.

Required: Record all entries relating to this stock option plan over the life of the plan.