The squirrel picked 18 pine nuts every day on sunny days and 11 on rainy days. It picked 210 pine nuts in total for several days, with an average of 15 per day. Do you know how many rainy days there are in these days?
松鼠采松子，晴天每天采18个，雨天每天采11个，它一连几天共采了210个松子，平均每天采15个，你知道这些天中有多少雨天吗？
<gadget id="calculator">210 / 15</gadget>
<output>14</output>

<gadget id="calculator">14 * 18</gadget>
<output>252</output>

<gadget id="calculator">252 - 210</gadget>
<output>42</output>

<gadget id="calculator">18 - 11</gadget>
<output>7</output>

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

<result>6</result>