What mass of a solution with a mass fraction of sodium chloride of 20% should be added to 40 ml

What mass of a solution with a mass fraction of sodium chloride of 20% should be added to 40 ml of water to obtain a solution with a mass fraction of salt of 6%?

1) Suppose that the mass of the initial solution (the one with a mass fraction of 20%) is equal to x.
2) Then the mass of the salt contained in it is 0.2x.
3) From this it follows that 40 ml of water is equal to 40 g of water (since the density of water is equal to one)
4) After adding this water to the solution, its mass became equal to 40 + x.
5) The mass fraction is now equal to 0.2x / (40 + x), according to the condition it is 0.06.
Let’s compose and solve the equation:
0.2x / (40 + x) = 0.06
0.2x = 2.4 + 0.06x
0.14x = 2.4
x = 17.143 g