An envelope has a length of 25 cm and a width of 12 cm. How many square centimeters of kraft paper is needed to make such an envelope? (Joints and seals are ignored)
一个信封，它的长是25厘米，宽12厘米．做这样的一个信封，至少需要多少平方厘米的牛皮纸？(接头与封口处忽略不计)
<gadget id="calculator">25 * 12 * 2</gadget>
<output>600</output>

<result>600</result>