Question 720057
from view of acid
3*.7=.2(3+x)
2.1=.6+.2x
1.5=.2x
x=7.5 pints

from view of water 
1*x+0.3*3=0.8(3+x)
1*x+0.9=2.4+0.8x
1x-0.8x=2.4-0.9
0.2x=1.5
x=7.5 pints

check
1*7.5+0.3*3=0.8(3+7.5)
7.5+0.9=0.8(10.5)
8.4=8.4

ok