Question 900947
x+2*.40=.7*(2+x)
x=2 gallons
check
2+.8=.7*4
2.8=2.8
from view of water
2*0.6=0.3*(2+x)
1.2=0.6+0.3*x
1.2-0.6=0.3*x
0.6=0.3*x
x=2
check
2*0.6=0.3*(2+x)
2*0.6=0.3*(4)
1.2=1.2
ok

or from view of acid
1*y+0.4*2=0.7(2+y)
1*y+0.8=1.4+0.7y
1*y-0.7y=1.4-0.8
0.3y=0.6
y=0.6/0.3
y=2