Final answer:
If Jones accepts a job paying $120 per week, his economic position will change by $72 per week. The effective marginal tax rate on Jones's earnings from this job would be 40%.
Step-by-step explanation:
To calculate how Jones's economic position will change if he accepts a job paying $120 per week, we need to determine the change in his benefits from the welfare programs. Each program grants him $150 per week, but benefits are reduced by 40 cents for each additional dollar he earns in the labor market. Therefore, for each dollar he earns, his benefits are reduced by 40 cents. If he accepts the job paying $120 per week, he will earn an additional $120 and his benefits will be reduced by $48 (40% of $120).
Therefore, Jones's economic position will change by $120 - $48 = $72 per week. He will be $72 per week better off than if he were unemployed and solely relying on welfare benefits.
The effective marginal tax rate on Jones's earnings from this job can be calculated by dividing the reduction in benefits ($48) by the increase in earnings ($120). This gives us a marginal tax rate of 40% ($48 / $120 = 0.4). Therefore, the effective marginal tax rate on Jones's earnings from this job would be 40%.