The number of goldfish in the 7 fish tanks is 9, 11, 10, 12, 21, 22 and 40 respectively. It is known that the fish in the same tank are of the same color, only one tank is black fish, and the rest are red and white, and the red is 5 times the white. Ask: How many black goldfish are there?
7只鱼缸所放金鱼的条数分别为9条、11条、10条、12条、21条、22条、40条．已知同一缸里的鱼同色，只有一缸是黑鱼，其余都是红色和白色，且红色是白色的5倍，问：黑色的金鱼有多少条．
<result>11</result>