Correct Answer - Option 2 : 2 days

**Given:**

A's time = 12 days

B's time = 8 days

B leaves after 4 days

**Calculation:**

Let total work be 24 (L.C.M of 12 and 8)

A's efficiency = 24/12 = 2 units/day

B's efficiency = 24/8 = 3 units/day

4 days work = (3 + 2) × 4 = 20 units

Remaining work = 4 units

required time = 4/2 = 2 days

**∴ The answer is 2 days**