Wang Ming and Ma Lin each read a literary book, Wang Ming reads 20 pages a day, and Ma Lin reads 15 pages a day, which happened to be finished at the same time. If Ma Lin reads 2 days in advance, Wang Ming reads 30 pages a day and can finish them at the same time. How many pages does Marin read in this book?
王明和马林各看一本文艺书，王明每天看20页，马林每天看15页，恰好能同时看完．如果马林提前2天看，王明每天看30页，也能同时看完．马林看的这本书有多少页？
<gadget id="calculator">30 - 20</gadget>
<output>10</output>

<gadget id="calculator">20 / 10</gadget>
<output>2</output>

<gadget id="calculator">2 * 2</gadget>
<output>4</output>

<gadget id="calculator">4 + 2</gadget>
<output>6</output>

<gadget id="calculator">15 * 6</gadget>
<output>90</output>

<result>90</result>