The perimeter of a rectangle is 30 cm, the width is 5 cm, what is the length in cm?
一长方形的周长是30厘米，宽5厘米，长是多少厘米．
<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">15 - 5</gadget>
<output>10</output>

<result>10</result>