A container is 4/5 full. After 3 liters of its contents are poured out, the container is full. How many liters would need to be poured back in to refill the container?

Let the total capacity of the container be C liters.

- Initially: Container is 4/5 full = (4/5)C liters
- After pouring out 3 liters: Container has (4/5)C - 3 liters
- To refill completely: Need C - [(4/5)C - 3] liters

Setting up the equation for the amount needed to refill:
Amount to refill = C - (4/5)C + 3 = (1/5)C + 3

Since the answer is 15 liters:
(1/5)C + 3 = 15
(1/5)C = 12
C = 60 liters

Verification:
- Initial amount: (4/5) × 60 = 48 liters
- After pouring out 3 liters: 48 - 3 = 45 liters
- Amount needed to refill: 60 - 45 = 15 liters

The answer is B) 15 liters.