Determine how much pure water should be mixed with 18 liters

Determine how much pure water should be mixed with 18 liters of a 15% solution of Hydrochloric acid to make a 12% solution of Hydrochloric acid.

let amount of water added =x litres

concentration of hydrocloric acid in pure water is 0%

pure water added to 18 liters of a 15% solution of Hydrochloric acid to make a 12% solution of Hydrochloric acid

x*(0/100) +18*(15/100) =(x+18)*12/100

0 +18*(15/100) =(x+18)*12/100

18*(15/100) =(x+18)*12/100

18*15 =(x+18)*12

(x+18)=18*15/12

x+18 =22.5

x=22.5-18

x=4.5

4.5 litres of pure water should be mixed with 18 liters of a 15% solution of Hydrochloric acid to make a 12% solution of Hydrochloric acid.