To make a pair of cuboid tin buckets without a cover, the length is 6 decimeters, the width is 3.5 decimeters, and the height is 3 decimeters. How much iron is needed at least?
做一对无盖的长方体铁皮水桶，长6分米，宽3.5分米，高3分米，至少需要多少铁皮？
<gadget id="calculator">6 * 3 * 2</gadget>
<output>36</output>

<gadget id="calculator">3.5 * 3 * 2</gadget>
<output>21</output>

<gadget id="calculator">6 * 3.5</gadget>
<output>21</output>

<gadget id="calculator">36 + 21 + 21</gadget>
<output>78</output>

<gadget id="calculator">78 * 2</gadget>
<output>156</output>

<result>156</result>