A rectangular piece of land has a perimeter of 120 meters and a length of 40 meters. What is the width of the piece of land?
一块长方形地的周长是120米，长是40米，这块地的宽是多少米？
<gadget id="calculator">120 / 2</gadget>
<output>60</output>

<gadget id="calculator">60 - 40</gadget>
<output>20</output>

<result>20</result>