The perimeter of a rectangle is 210dm and its length is 80dm. What is the area of this rectangle in square meters?
一个长方形的地周长是210dm，长是80dm．这个长方形的面积是多少平方米？
<gadget id="calculator">210 / 2</gadget>
<output>105</output>

<gadget id="calculator">105 - 80</gadget>
<output>25</output>

<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">80 * (1/4)</gadget>
<output>20</output>

<result>20</result>