Li Qiang reads an extracurricular book. He read 10% of the whole book on the first day, 35 pages on the second day, and 7 pages on the third day. He just read 40% of the whole book in these three days. How much is this extracurricular book? Page?
李强读一本课外读物，第一天读了全书的10%，第二天读了35页，第三天读了7页，这三天正好读了全书的40%，这本课外读物有多少页？
<gadget id="calculator">35 + 7</gadget>
<output>42</output>

<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

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

<gadget id="calculator">42 / (3/10)</gadget>
<output>140</output>

<result>140</result>