A cuboid glass fish tank without a cover is 3 decimeters long, 2.5 decimeters wide, and 4 decimeters high. How many square decimeters of glass do you need to make a pair of such glass fish tanks?
一个长方体的无盖玻璃鱼缸，长3分米，宽2.5分米，高4分米．做一对这样的玻璃鱼缸至少需要多少平方分米的玻璃？
<gadget id="calculator">3 * 2.5</gadget>
<output>7.5</output>

<gadget id="calculator">3 * 4 * 2</gadget>
<output>24</output>

<gadget id="calculator">2.5 * 4 * 2</gadget>
<output>20</output>

<gadget id="calculator">7.5 + 24 + 20</gadget>
<output>51.5</output>

<gadget id="calculator">51.5 * 2</gadget>
<output>103</output>

<result>103</result>