There are two piles of Chinese cabbage, the first pile has 87, and the second pile has 69. How many cabbages are taken from the first pile to the second pile so that the number of cabbages in the second pile is three times that of the first pile.
有两堆大白菜，第一堆有87棵，第二堆有69棵，从第一堆拿多少棵白菜到第二堆才可使第二堆的白菜数是第一堆的3倍．
<gadget id="calculator">87 + 69</gadget>
<output>156</output>

<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<gadget id="calculator">156 / 4</gadget>
<output>39</output>

<gadget id="calculator">87 - 39</gadget>
<output>48</output>

<result>48</result>