To keep the skin white and smooth, it is customary to take salt baths for the face and hands

To keep the skin white and smooth, it is customary to take salt baths for the face and hands. What mass of table salt should be dissolved in 250 g of water to make a 10% solution?

Given:
m (H2O) = 250 g
ω (NaCl) = 10%

Find:
m (NaCl) -?

Solution:
1) Take that m (NaCl) = (x) r;
2) Calculate the mass of the sodium chloride solution:
m solution (NaCl) = m (NaCl) * 100% / ω (NaCl) = x * 100% / 10% = (10x) g;
3) Calculate the mass of the sodium chloride solution in another way:
m solution (NaCl) = m (NaCl) + m (H2O) = (x + 250) g;
4) Make an equation and solve it:
m solution (NaCl) = m solution (NaCl);
10x = x + 250;
9x = 250;
x = 27.8;
m (NaCl) = x = 27.8 g.

Answer: The mass of NaCl is 27.8 g.