Answer
4.5 liters of 4% solution and 7.5 liters of 12% solution
Work Step by Step
$x+y=12$
$.04*x+.12*y=12*.09$
$.04*x+.12*y=12*.09$
$.04x+.12y=1.08$
$.04x+.12y=1.08$
$25*(.04x+.12y=1.08)$
$x+3y=27$
$x+y=12$
$x+3y=27$
$x+3y-(x+y)=27-12$
$x+3y-x-y=15$
$2y=15$
$2y/2=15/2$
$y=7.5$
$x+y=12$
$x+7.5=12$
$x=4.5$