There are 98 books on the upper shelf and 40 books on the lower shelf. If there are 18 more books on the upper shelf than on the lower shelf, how many books must be taken from the upper shelf to the lower shelf?
书架上层有98本书，下层有40本书，要使上层的书比下层多18本，那么就要从上层拿多少本书到下层？
<gadget id="calculator">40 - 18</gadget>
<output>22</output>

<gadget id="calculator">98 + 22</gadget>
<output>120</output>

<gadget id="calculator">120 / 2</gadget>
<output>60</output>

<gadget id="calculator">60 + 18</gadget>
<output>78</output>

<gadget id="calculator">98 - 78</gadget>
<output>20</output>

<result>20</result>