There are 4 liters of water in bucket A and 13 liters in bucket B. After adding the same amount of water to both buckets, the water in bucket B will be 3 times the water in bucket A (the water will not overflow). So, how many liters of water are added to each bucket?
甲桶内有水4升，乙桶内有水13升，向两个桶内加入同样多的水后，乙桶内的水是甲桶内的水的3倍(水不溢出)．那么，向每个桶内加入的水是多少升？
<gadget id="calculator">3 * 4</gadget>
<output>12</output>

<gadget id="calculator">13 - 12</gadget>
<output>1</output>

<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<result>1/2 = around 0.5</result>