There are 40 black rabbits and 7 white rabbits in a rabbit farm. If the number of black rabbits is 6 times that of white rabbits and the white rabbits remain unchanged, how many black rabbits should there be?
养兔场有黑兔40只，白兔7只，要使黑兔的只数是白兔的6倍，白兔保持不变，黑兔应当多少只．
<gadget id="calculator">7 * 6</gadget>
<output>42</output>

<result>42</result>