There are 40 white rabbits and black rabbits in total. The number of black rabbits is 3/5 of that of white rabbits. How many black rabbits are there?
白兔和黑兔共有40只，黑兔的只数是白兔的(3/5)，黑兔有多少只？
<gadget id="calculator">3 + 5</gadget>
<output>8</output>

<gadget id="calculator">3 / 8</gadget>
<output>3/8 = around 0.375</output>

<gadget id="calculator">40 * (3/8)</gadget>
<output>15</output>

<result>15</result>