There are 16 black, white and red beads in a box, and the number of white beads is 7 times that of red beads. How many black beads are there in the box?
一个盒子里有黑、白、红三色的珠子共16颗，其中白珠子的颗数是红珠子的7倍．盒子里有黑珠子多少颗．
<gadget id="calculator">16 - 1 - 7</gadget>
<output>8</output>

<result>8</result>