An extra-curricular book with a total of 180 pages, Xiaohua has already read (1/4) of the whole book, how many pages are left unread?
一本课外书，共180页，小华已经读了全书的(1/4)，还有多少页没读？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">180 * (1/4)</gadget>
<output>45</output>

<gadget id="calculator">180 - 45</gadget>
<output>135</output>

<result>135</result>