The perimeter of a rectangle is 30 cm, the width is 6 cm, what is the length in cm
一个长方形的周长是30厘米，宽6厘米，长多少厘米
<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">15 - 6</gadget>
<output>9</output>

<result>9</result>