There are red and white balls in a pile of balls, 48 red balls out of the 50 balls taken out for the first time, and 6 red balls out of 7 balls taken out each time, so that the red balls out of the taken out balls are equal to 90% , then how many times can be taken at most.
一堆球中有红白两种球，第一次取出的50个球中有48个红球，以后每次取出7个球中6个红球，要使取出的球中红球等于90%，那么最多可以取多少次．
<result>11</result>