classroom is 15 meters long, 12 meters wide, and 4 meters high. The area of doors and windows occupies 42 square meters. If you want to paint this classroom, how many square meters will the painted area be? (top surface not painted)
一间教室长15米，宽12米，高4米，门窗的面积占42平方米，如果要粉刷这间教室，粉刷的面积是得数平方米？(顶面不粉刷)
<gadget id="calculator">15 * 4</gadget>
<output>60</output>

<gadget id="calculator">12 * 4</gadget>
<output>48</output>

<gadget id="calculator">60 + 48</gadget>
<output>108</output>

<gadget id="calculator">108 * 2</gadget>
<output>216</output>

<gadget id="calculator">216 - 42</gadget>
<output>174</output>

<result>174</result>