A book with 150 pages, Dongdong read it for 3 days, 5 pages a day, how many pages did he start reading on the fourth day.
一本书150页，东东看了3天，每天看5页，他第四天从第多少页看起．
<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<gadget id="calculator">15 + 1</gadget>
<output>16</output>

<result>16</result>