A water supply company in a certain city stipulates: "The water consumption per person per month does not exceed 2 tons, and the fee is 0.9 yuan per ton. The part that exceeds 2 tons is charged at 2 yuan per ton." The water fee is 19 yuan, how many tons of water is shared by Xiao Ming's family?
某市自来水公司规定："每人每月用水量不超过2吨，按每吨0.9元收费．超过2吨的部分，每吨按2元收费．"小明家一共5口人，上月共交水费19元，小明家共用水多少吨．
<gadget id="calculator">0.9 * 2 * 5</gadget>
<output>9</output>

<gadget id="calculator">19 - 9</gadget>
<output>10</output>

<gadget id="calculator">10 / 2</gadget>
<output>5</output>

<gadget id="calculator">2 * 5</gadget>
<output>10</output>

<gadget id="calculator">5 + 10</gadget>
<output>15</output>

<result>15</result>