There are 160 white rabbits and 120 gray rabbits in the farm, and the number of black rabbits is three times the total number of white rabbits and gray rabbits. How many black rabbits are there?
饲养场养了160只白兔、120只灰兔，黑兔的只数是白兔和灰兔总数的3倍，养黑兔多少只？
<gadget id="calculator">160 + 120</gadget>
<output>280</output>

<gadget id="calculator">280 * 3</gadget>
<output>840</output>

<result>840</result>