We need to find out how much water there is in the mixture.
0.0189 and 0.05 are the converted percentages.
0.0189×4200=79.38 gallons; 0.05×1200=60 gallons,
so the total amount of water is 139.38 gallons in 4200+1200=5400 gallons of mixture.
Therefore the percentage of water in the mixture is 139.38/5400×100=2.58% approx.