There are 15 white rabbits, 3 times less than black rabbits, how many black rabbits are there?
白兔是15只，比黑兔的3倍少3只，黑兔是多少只．
<gadget id="calculator">15 + 3</gadget>
<output>18</output>

<gadget id="calculator">18 / 3</gadget>
<output>6</output>

<result>6</result>