The fifth grade students used their spare time to wipe the windows of the school classrooms. In the first week, they wiped 40% of the windows of the classrooms in the school. In the second week, they wiped the windows of 12 classrooms. The windows of 6 classrooms were not wiped. How many classrooms are there? (column equation solution)
五年级的同学利用课余时间擦学校教室的窗户玻璃，第一周擦了全校教室窗户玻璃的40%，第二周擦了12间教室窗户玻璃，还剩6间教室窗户玻璃没有擦，学校一共有多少间教室？(列方程解答)
<gadget id="calculator">18 / 0.6</gadget>
<output>30</output>

<result>30</result>