Liu Xiao reads a world famous book. He reads an average of 28 pages a day. After 15 days of reading, there are still 87 pages left. How many pages does this famous book have?
刘晓读一本世界名著，平均每天读28页，读了15天，还有87页没有读，这本名著共有多少页？
<gadget id="calculator">28 * 15</gadget>
<output>420</output>

<gadget id="calculator">420 + 87</gadget>
<output>507</output>

<result>507</result>