The perimeter of a rectangle is 90 cm, the width is 20 cm, what is the length in cm? (solution by equation)
一个长方形的周长是90厘米，宽是20厘米，长是多少厘米？(用方程解)
<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<gadget id="calculator">90 - 40</gadget>
<output>50</output>

<gadget id="calculator">50 / 2</gadget>
<output>25</output>

<result>25</result>