A 5% salt solution weighing 300 g was filled with 75 g of salt. Find the percentage of salt in the new solution.

1. Mass of the solution: M = 300 grams;

2. The amount of salt as a percentage: Ps = 5%;

3. Amount of added salt: Md = 75 grams;

4. The amount of salt in the solution: Ms = Ps * M / 100 = 5 * 300/100 = 15 g;

5. The amount of salt in the new solution: Msn = Ms + Md = 15 + 75 = 90 g;

6. The mass of the new solution: Mn = M + Md = 300 + 75 = 375 g;

7. The amount of salt as a percentage in the new solution: Psn = (Msn * 100) / Mn = (90 * 100) / 375 = 9000/375 = 24%.

Answer: the salt content in the new solution is 24%.