Answer:
16 men
Step-by-step explanation:
4 men : 8 days
8 men : 4 days → double the men is half the time which is 4 days
16 men : 2 days —-> and so double 8 men will complete the job in 2 days
Hence 16 men is required to complete the job. Since you already have 4 workers you will need 12 additional men.