Question 815803
 point of view of water

x+.80*30=.85(x+30)
x+24. = 0.85 (x+30)
x+24. = 0.85 x+25.5
0.15 x=1.5
x = 10
from the point of view of chlorine 
.20*(30)=.15(x+30)
x = 10