A rectangle has a length of 7 decimeters and a perimeter of 20 decimeters, what is its width? What is the column
一个长方形长7分米，周长是20分米，它的宽是多少分米？列式为多少
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

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

<result>3</result>