Xiaoli reads a book, read 20% of it on the first day, 30% of it on the second day, and read 15 pages more on the second day than on the first day. How many pages did Mary read on the first day?
小丽读一本书，第一天读了它的20%，第二天读了它的30%，第二天比第一天多读了15页．小丽第一天读了多少页？
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(3/10) - (1/5)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">15 / (1/10)</gadget>
<output>150</output>

<gadget id="calculator">150 * (1/5)</gadget>
<output>30</output>

<result>30</result>