A storybook is 20 cm long, 15 cm wide, and 2 cm thick. How many ribbons are needed to tie up these three books? (15 cm at the joint)
一种故事书长20厘米，宽15厘米，厚2厘米，把这样的3本书扎起来，一共需要多少彩带？(接头处15厘米)
<gadget id="calculator">20 * 2</gadget>
<output>40</output>

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

<gadget id="calculator">2 * 3</gadget>
<output>6</output>

<gadget id="calculator">6 * 4</gadget>
<output>24</output>

<gadget id="calculator">40 + 30 + 24 + 15</gadget>
<output>109</output>

<result>109</result>