Question 1024133
Call the amount of 25% solution, x.  Then the amount of 75% solution would have to be 90-x.  The setup is like this...
.25x + .75(90-x) = .35(90)
Now solve this...
.25x + 67.5 - .75x = 31.5
-.5x = -36
x = 72 ounces of 25% solution which means
90-x = 18 ounces of 75% solution