Su Hua reads a 72-page book, and reads (1/4) of the whole book on the first day, how many more pages does it take to read exactly half of the book?
苏华看一本72页的书，第一天看了全书的(1/4)，再看多少页就正好看了这本书的一半？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/2) - (1/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">72 * (1/4)</gadget>
<output>18</output>

<result>18</result>