The percent as a decimal (divide the percent by 100) times the amount is the amount of OJ.
Amount for the 60% + amount for the 10% = amount for the 50%
Here's an answer rather than a question.
.6x + .1*11 = .5(11+x)
.6x + 1.1 = 5.5 + .5x
.1x = 4.4
x = 4.4/.1 = 44 gallons.