Use rectangles with a length of 20 cm and a width of 12 cm to assemble a large square. How many such rectangles are needed at least?
用长20厘米，宽12厘米的长方形去拼一个大正方形，至少需要多少个这样的长方形？
<gadget id="calculator">2 * 2 * 3 * 5</gadget>
<output>60</output>

<gadget id="calculator">60 / 12</gadget>
<output>5</output>

<gadget id="calculator">60 / 20</gadget>
<output>3</output>

<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<result>15</result>