A classroom with a length of 20 meters, a width of 15 meters, and a height of 4.5 meters needs to paint the surrounding walls and ceiling. Excluding doors and windows of 10.5 square meters, 500 grams of paint is used per square meter. How many kilograms of paint are needed in total?
一间长20米，宽15米，高4.5米的教室，要粉刷四周墙壁和顶棚，除却门窗10.5平方米，每平方米用涂料500克，一共需要涂料多少千克？
<gadget id="calculator">20 * 15</gadget>
<output>300</output>

<gadget id="calculator">20 * 4.5 * 2</gadget>
<output>180</output>

<gadget id="calculator">15 * 4.5 * 2</gadget>
<output>135</output>

<gadget id="calculator">135 - 10.5</gadget>
<output>124.5</output>

<gadget id="calculator">300 + 180 + 124.5</gadget>
<output>604.5</output>

<gadget id="calculator">604.5 / 1_000</gadget>
<output>0.6045</output>

<gadget id="calculator">500 * 0.6045</gadget>
<output>302.25</output>

<result>302.25</result>