Question 273484
These types of problems help to make a chart 


First find the number of liters for the 90%, then the 40%, and then the combined mixture and you will get your first equation. It should be x+y=100 since we don't know the amount of either the 90% or the 40%

Next determine the amount of alcohol that is in each solution and multiply that by the amount of liters in each solution. This will make your second equation and it should be .9x+.4y=.6(100)

Use the elimination method to solve from here

x+y=100 (multiply both sides of the first equation by -.4)
.9x+.4y=60
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This is much easier to do on paper than on the computer. if you still con't figure it out, reply back with an email address and I will work it out on paper and send a scanned copy to you.