A piece of iron wire can just form a rectangle with a length of 7dm and a width of 3dm. If this iron wire forms a square, what is its area?
一根铁丝正好可以围成一个长7dm，宽3dm的长方形，如果用这根铁丝围成一个正方形，它的面积有多大？
<gadget id="calculator">7 + 3</gadget>
<output>10</output>

<gadget id="calculator">10 * 2</gadget>
<output>20</output>

<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">5 * 5</gadget>
<output>25</output>

<result>25</result>