Lingling reads "The King of Stories", 6 pages a day for 3 days, how many pages should she start reading on the 4th day.
玲玲看《故事大王》，每天看6页，看了3天，第4天该从第多少页看起．
<gadget id="calculator">6 * 3</gadget>
<output>18</output>

<gadget id="calculator">18 + 1</gadget>
<output>19</output>

<result>19</result>