A square vegetable field has the same perimeter as a rectangular vegetable field. The side length of a square vegetable field is 40 meters, and the length of a rectangular vegetable field is 50 meters. How many meters is the width of the rectangular vegetable field?
一块正方形菜地与一块长方形菜地的周长相等．正方形菜地边长40米，长方形菜地长50米，长方形菜地宽多少米？
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">40 * 2</gadget>
<output>80</output>

<gadget id="calculator">80 - 50</gadget>
<output>30</output>

<result>30</result>