A rectangle with a length of 15 cm and a perimeter of 50 cm is its width in cm.
一个长15厘米的长方形，它的周长是50厘米，它的宽是多少厘米．
<gadget id="calculator">50 / 2</gadget>
<output>25</output>

<gadget id="calculator">25 - 15</gadget>
<output>10</output>

<result>10</result>