Question 1150645
Description is incomplete.  
350 Liters of what finished percent acid?



If result is 350 liters of some number p percent acid, then
x liters of 70%
350-x liters of 20%
{{{70x+20(350-x)=p*350}}}


{{{7x+2(350-x)=35p}}}
{{{7x+2*350-2x=35p}}}
{{{5x+2*350=35p}}}
{{{5x=35p-2*350}}}
{{{x=7p-140}}}
You finish from here.  You need to know the given finished percent acid, p; and then you can evaluate  x and 350-x.