6 Suppose the value of marginal product for all workers in a firm is $20 per hour. Shirking is a major problem in the firm, so the manager of the firm proposes to institute a scheme of deferred wages. Assume that the wage of a worker is determined by the formula:

Assuming that the discount rate is zero and that all workers enter the firm at the age of 25. What will be the mandatory retirement age in this firm?