The mother squirrel picks pine cones. She picks 20 pine cones a day on sunny days, but only 13 pine cones on rainy days. She has picked 112 pine cones for several days, and she picks 16 pine cones on average. How many days does it rain?
松鼠妈妈采摘松果，晴天每天摘20个，雨天每天只能摘13个，它一连几天工采了112个松果，平均每天摘16个，那么这几天有几天下雨？
<gadget id="calculator">112 / 16</gadget>
<output>7</output>

<gadget id="calculator">20 * 7</gadget>
<output>140</output>

<gadget id="calculator">140 - 112</gadget>
<output>28</output>

<gadget id="calculator">20 - 13</gadget>
<output>7</output>

<gadget id="calculator">28 / 7</gadget>
<output>4</output>

<result>4</result>