Use small rectangles with a length of 15cm and a width of 12cm to form a large square. How many such rectangles are needed at least?
用长15cm、宽12cm的小长方形拼成一个大正方形，最少需要多少个这样的长方形？
<gadget id="calculator">3 * 5 * 2 * 2</gadget>
<output>60</output>

<gadget id="calculator">60 / 15</gadget>
<output>4</output>

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

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

<result>20</result>