Water is the fountain of life. In order to encourage water conservation, a certain city has formulated a water standard for residents. The standard is set according to the number of people in a household, and the portion exceeding the standard will be charged an increase. Assume that the water fee for a family of three is 1.3 yuan per cubic meter within the water standard, and 2.9 yuan per cubic meter for the part exceeding the standard. A family of three used 12 cubic meters of water in June and paid a water fee of 22 yuan. What is the standard monthly water consumption of a family of three in this city?
水是生命之泉．为鼓励节约用水，某市制定了居民用水标准，标准依一户的人口数定的，超过标准部分加价收费．设三口之家用水标准内部分每立方米水费为1.3元，超过标准部分每立方米水费为2.9元．某三口之家六月份用水12立方米，交水费22元，求该市三口之家每月的标准用水量是多少？
<gadget id="calculator">2.9 * 12</gadget>
<output>34.8</output>

<gadget id="calculator">34.8 - 22</gadget>
<output>12.8</output>

<gadget id="calculator">2.9 - 1.3</gadget>
<output>1.6</output>

<gadget id="calculator">12.8 / 1.6</gadget>
<output>8</output>

<result>8</result>