At least how many rectangular planks with a length of 21 cm and a width of 18 cm are needed to form a square.
至少要用多少块长为21厘米、宽为18厘米的长方形木板才能拼成一个正方形．
<gadget id="calculator">2 * 3 * 3 * 7</gadget>
<output>126</output>

<gadget id="calculator">126 / 21</gadget>
<output>6</output>

<gadget id="calculator">126 / 18</gadget>
<output>7</output>

<gadget id="calculator">6 * 7</gadget>
<output>42</output>

<result>42</result>