Distribute m apples to n children. If each person has 5 apples, there will be 1 remaining; if each person has 6 apples, there will be a shortage of 3, then mn=how much.
m个苹果分给n个小朋友，若每人5个，则余1个；若每人6个，则缺3个，则mn=多少．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<gadget id="calculator">6 - 5</gadget>
<output>1</output>

<gadget id="calculator">4 / 1</gadget>
<output>4</output>

<gadget id="calculator">4 * 5</gadget>
<output>20</output>

<gadget id="calculator">20 + 1</gadget>
<output>21</output>

<gadget id="calculator">4 * 21</gadget>
<output>84</output>

<result>84</result>