Li Hua reads a book. He read the whole book (1/5) on the first day, 18 pages on the second day, and exactly half of the book in two days. How many pages did Li Hua read on the first day?
李华读一本书，第一天读了全书的(1/5)，第二天读了18页，两天正好读了这本书的一半，李华第一天读了多少页？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/2) - (1/5)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">18 / (3/10)</gadget>
<output>60</output>

<gadget id="calculator">60 * (1/5)</gadget>
<output>12</output>

<result>12</result>