Labor Economics 5th Edition by George Borjas

Exercise 15

All workers start working for a particular firm when they are 20 years old. The value of each worker's marginal product is $18 per hour. In order to prevent shirking on the job, a delayed-compensation scheme is imposed. In particular, the wage level at every level of seniority is determined by:
Wage = $10 + (.4 × Years in the firm).
Suppose also that the discount rate is zero for all workers. What will be the mandatory retirement age under the compensation scheme (Hint: Use a spreadsheet.)