The mathematics textbook is a cuboid. The measured length is about 21 cm, the width is about 14.5 cm, and the thickness of the textbook is about 0.6 cm. Cut a piece of plastic sheet that is equal in size to the sum of the top and bottom sides of the textbook and the edge of the book to make the book cover, find the area of the cut plastic sheet.
数学课本是一个长方体，现量得长约是21厘米，宽约是14.5厘米，课本厚约是0.6厘米．要剪一块和课本上、下两个面和书棱面的和的大小相等的塑料布做书皮，求裁剪的塑料布的面积．
<gadget id="calculator">21 * 14.5 * 2</gadget>
<output>609</output>

<gadget id="calculator">21 * 0.6</gadget>
<output>12.6</output>

<gadget id="calculator">609 + 12.6</gadget>
<output>621.6</output>

<result>621.6</result>