2 white balls are equal to 4 black balls, 3 black balls are equal to 1 white ball plus 1 yellow ball, how many yellow balls are equal to 3 white balls plus 4 black balls.
2只白球与4只黑球的重量相等，3只黑球的重量等于1只白球加1只黄球，多少只黄球的重量等于3只白球加4只黑球．
<result>10</result>