In order to encourage residents to save water, the water company stipulates that each household will be charged 2.5 yuan per ton for water consumption within 10 tons (including 10 tons) per month; if it exceeds 10 tons, the excess tonnage will be charged at 4.5 yuan per ton. Teacher Wang’s family paid a total of 34 yuan for water last month. How many tons of water was used by Teacher Wang’s family last month?
为鼓励居民节约用水，自来水公司规定：每户每月用水10吨以内(含10吨)，按每吨2.5元收费；超过10吨的，其超出的吨数按每吨4.5元收费．王老师家上月共交水费34元，王老师家上月用水多少吨？
<gadget id="calculator">2.5 * 10</gadget>
<output>25</output>

<gadget id="calculator">34 - 25</gadget>
<output>9</output>

<gadget id="calculator">9 / 4.5</gadget>
<output>2</output>

<gadget id="calculator">2 + 10</gadget>
<output>12</output>

<result>12</result>