A rope encloses exactly a rectangle 40 decimeters long and 30 decimeters wide. If you surround a square with this rope, what is the area of the square?
一根绳子恰好围成一个长40分米、宽30分米的长方形．如果用这根绳子围城一个正方形，这个正方形的面积是多少？
<gadget id="calculator">40 + 30</gadget>
<output>70</output>

<gadget id="calculator">2 / 4</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">70 * (1/2)</gadget>
<output>35</output>

<gadget id="calculator">35 * 35</gadget>
<output>1_225</output>

<result>1_225</result>