Question 904744
0.8*x+0.25*6=0.55(6+x)
0.8*x+1.5=3.3+0.55x
0.8x-0.55x=3.3-1.5
0.25x=1.8

x=7.2 liter of 80% is added to 6 liter of 25%  to get  13.2 liter  at 55%
check
0.8*7.2+0.25*6=0.55(6+7.2)
5.76+1.5=0.55(13.2)
7.26=7.26
ok