The kitten goes fishing by the river, and catches 6 fishes every day on sunny days, and 9 fishes every day on rainy days, for 6 consecutive days, with an average of 7 fishes every day. So, how many days are there sunny days?
小猫去河边钓鱼，晴天每天钓6条，雨天每天钓9条，一连钓6天，平均每天钓7条，那么，有几天晴天？
<gadget id="calculator">6 * 7</gadget>
<output>42</output>

<gadget id="calculator">6 * 6</gadget>
<output>36</output>

<gadget id="calculator">42 - 36</gadget>
<output>6</output>

<gadget id="calculator">9 - 6</gadget>
<output>3</output>

<gadget id="calculator">6 / 3</gadget>
<output>2</output>

<gadget id="calculator">6 - 2</gadget>
<output>4</output>

<result>4</result>