A classroom is 9 meters long, 6 meters wide, and 4 meters high. If you paint its roof and walls, and deduct the door and window area of 24 square meters, if you use 0.2 kilograms of wall powder per square meter, how many kilograms of wall powder are needed in total?
一间教室长9米，宽6米，高4米，粉刷它的屋顶和四壁，扣除门窗面积24平方米，如果每平方米用刷墙粉0.2千克，一共需要刷墙粉多少千克？
<gadget id="calculator">9 * 6</gadget>
<output>54</output>

<gadget id="calculator">9 * 4</gadget>
<output>36</output>

<gadget id="calculator">6 * 4</gadget>
<output>24</output>

<gadget id="calculator">54 + 36 + 24</gadget>
<output>114</output>

<gadget id="calculator">114 * 2</gadget>
<output>228</output>

<gadget id="calculator">228 - 54 - 24</gadget>
<output>150</output>

<gadget id="calculator">150 * 0.2</gadget>
<output>30</output>

<result>30</result>