Calculate w in the islands obtained by dissolving 20 g of salt in 150 g of water.

To solve this problem, you will need to draw up an equation.
Let x be the mass fraction of a substance in a solution, then the mass of the resulting solution = 150 + 120 (grams), we compose the equation
20 + 150 * 0 = 170 * x (since the salt content in water is 0, then its mass fraction is 0)
170 * x = 20
x = 20/170
x = 0.118
This means the mass fraction of the substance in the solution = 11.8%