Zhang Haoran read a popular science book, and he has already read 42 pages. The ratio of pages he has read to pages he has not read is 3:7. How many pages does this textbook have?
张浩然看一本科普书，已经看了42页，已经看的与没看的页数比是3：7．这本科普书一共有多少页？
<gadget id="calculator">3 + 7</gadget>
<output>10</output>

<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

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

<result>140</result>