A classroom is 20 meters long, 8 meters wide, and 3.5 meters high. The blackboard, doors and windows cover an area of 56 square meters. The walls and ceiling need to be painted, with an average of 0.25 kilograms of paint per square meter. How many kilograms of paint are needed in total?
一间教室长20米，宽8米，高3.5米，黑板及门窗面积为56平方米，要粉刷四壁和顶棚，平均每平方米用涂料0.25千克，一共需要涂料多少千克？
<gadget id="calculator">20 * 8</gadget>
<output>160</output>

<gadget id="calculator">20 * 3.5 * 2</gadget>
<output>140</output>

<gadget id="calculator">8 * 3.5 * 2</gadget>
<output>56</output>

<gadget id="calculator">56 - 56</gadget>
<output>0</output>

<gadget id="calculator">160 + 140 + 0</gadget>
<output>300</output>

<gadget id="calculator">0.25 * 300</gadget>
<output>75</output>

<result>75</result>