There is some solution of salt in water. After adding three liters of water to the solution, the salt concentration decreased

There is some solution of salt in water. After adding three liters of water to the solution, the salt concentration decreased by 15%, and after evaporation of five liters of water from the resulting solution, the salt concentration became 3 times higher than the initial one. Find the concentration of salt in the original solution, considering the mass of 1 liter of water equal to 1 kg.

Decision:
1) Take the mass of the initial solution as (x) kg, and the mass of salt in it as (y) kg. Then the concentration of the substance will be (y / x)%;

2) After adding water, the mass of the solution turned out to be (x + 3) kg, the mass of salt in it remained the same – (y) kg. Then the concentration of the substance will be (y / (x + 3))%, while it has become 15% less than the original, that is
(y / x) – (y / (x + 3)) = 15%;

3) After evaporation of water, the mass of the solution was (x + 3 – 5) kg, the mass of salt in it remained the same – (y) kg. Then the concentration of the substance will be (y / (x + 3 – 5))%, while it has increased 3 times from the original, that is
(y / (x + 3 – 5)) / (y / x) = 3;

4) Make up a system of equations and solve:
To simplify calculations, we will convert the concentration from percent to units: 15% = 0.15;
(y / x) – (y / (x + 3)) = 0.15;
(y / (x + 3 – 5)) / (y / x) = 3;
We solve the second equation:
(y / (x + 3 – 5)) / (y / x) = 3;
(y / (x – 2)) * (x / y) = 3;
x / (x – 2) = 3;
x = (x – 2) * 3;
x = 3x – 6;
2x = 6;
x = 3 – found the mass of the original solution;
We solve the first equation taking into account the result of solving the second:
(y / x) – (y / (x + 3)) = 0.15;
(y / 3) – (y / (3 + 3)) = 0.15;
(y / 3) – (y / 6) = 0.15;
(2y – y) / 6 = 0.15;
y / 6 = 0.15;
y = 0.15 * 6;
y = 0.9 – found the mass of salt in the original solution;

5) Find the concentration of salt in the original solution:
ω (salt) = y * 100% / x = 0.9 * 100% / 3 = 30%.

Answer: The salt concentration in the original solution was 30%.