How much glass is needed to make a cuboid fish tank without a cover whose length, width and height are 40 cm, 30 cm and 15 cm respectively?
做一个长、宽、高分别是40厘米、30厘米、15厘米的无盖长方体鱼缸，需要多少玻璃？
<gadget id="calculator">40 * 30</gadget>
<output>1_200</output>

<gadget id="calculator">40 * 15 * 2</gadget>
<output>1_200</output>

<gadget id="calculator">30 * 15 * 2</gadget>
<output>900</output>

<gadget id="calculator">1_200 + 1_200 + 900</gadget>
<output>3_300</output>

<result>3_300</result>