A25% brine solution was mixed with an 18% brine solution to produce a 20% brine solution. how much of the 25% solution and how much of the 18% solution was used to produce 28 l of the 20% solution

8L of 25% brine solution 
20L of 18% brine solution  
Let's assign the variable X to represent the amount of 25% brine solution that was used. We then have (28-X) to represent the amount of 18% solution and we can create the following equation: 
 0.25X + 0.18(28-X) = 0.20*28 
 Now solve for X.
 0.25X + 0.18(28-X) = 0.20*28
 0.25X + 0.18*28 - 0.18X = 0.20*28
 0.07X + 0.18*28 = 0.20*28
 0.07X = 0.20*28 - 0.18*28
 0.07X = (0.20 - 0.18)*28
 0.07X = 0.02*28
 0.07X = 0.56
 X = 8 
 So we used 8 L of the 25% brine solution. And 28 - 8 = 20 L of the 18% solution.

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Compound with sulfer  is bright red