There are 20 classes in a school. The school plans to paint the walls and roof of the classroom during the holidays. It is known that the length of a classroom is 8 meters, the width is 7 meters, and the height is 3 meters. The area after deducting the doors and windows is 10.91 square meters, and the blackboard area is 4.09 square meters. If one kilogram of paint is needed for every 5 square meters of wall surface, please ask the school About how many kilograms of paint should be purchased?
某校共有20个班级．学校计划要在假期粉刷教室的四壁和屋顶．已知一间教室的长是8米，宽7米，高是3米，扣除门窗的面积10.91平方米，黑板面积4.09平方米，如果每粉刷5平方米的墙面需要一千克涂料，请问学校大约要购置多少千克的涂料？
<gadget id="calculator">8 * 7</gadget>
<output>56</output>

<gadget id="calculator">8 * 3 * 2</gadget>
<output>48</output>

<gadget id="calculator">7 * 3 * 2</gadget>
<output>42</output>

<gadget id="calculator">42 - 10.91 - 4.09</gadget>
<output>27</output>

<gadget id="calculator">56 + 48 + 27</gadget>
<output>131</output>

<gadget id="calculator">20 / 5</gadget>
<output>4</output>

<gadget id="calculator">131 * 4</gadget>
<output>524</output>

<result>524</result>