It is known that the perimeter of a rectangle is 68 cm, the length of one side is 21 cm, and the length of the other side is how many cm.
已知一个长方形周长是68厘米，其中一条边长是21厘米，另一条边长是多少厘米．
<gadget id="calculator">68 / 2</gadget>
<output>34</output>

<gadget id="calculator">34 - 21</gadget>
<output>13</output>

<result>13</result>