A rectangular piece of land is 7 meters long and 20 meters in circumference. What is the width in meters?
一块长方形地，长7米，周长20米，宽是多少米．
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 - 7</gadget>
<output>3</output>

<result>3</result>