Water fee adjustment publicity: each household uses less than 15 tons of water per month (including 15 tons), and is charged 1.2 yuan per ton. If it exceeds 15 tons, it is charged at 5 yuan per ton. Mr. Zhu's water bill this month is 33 yuan. How many tons of water did Mr. Zhu use at home this month?
水费调整公示：每户每月用水15吨以下(含15吨)，按每吨1.2元收费，超过15吨，超过的部分按每吨5元收费．朱老师这个月的水费是33元，这个月朱老师家用了多少吨水？
<gadget id="calculator">1.2 * 15</gadget>
<output>18</output>

<gadget id="calculator">33 - 18</gadget>
<output>15</output>

<gadget id="calculator">15 / 5</gadget>
<output>3</output>

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

<result>18</result>