In order to encourage residents to save water, the water company stipulates that each household uses less than 15 tons of water per month (including 15 tons), and charges 2.2 yuan per ton; if it exceeds 15 tons, the excess tonnage is charged at 4 yuan per ton. Xiao Ming’s family shared 18 tons of tap water last month. How much should I pay for the water?
为了鼓励居民节约水，自来水公司规定，每户每月用水15吨以内(含15吨)，按每吨2.2元；超过15吨的，其超出部分的吨数按每吨4元收费．小明家上月共用18吨自来水，应该交水费多少元？
<gadget id="calculator">2.2 * 15</gadget>
<output>33</output>

<gadget id="calculator">18 - 15</gadget>
<output>3</output>

<gadget id="calculator">4 * 3</gadget>
<output>12</output>

<gadget id="calculator">33 + 12</gadget>
<output>45</output>

<result>45</result>