At t°C, the NaOH solution with a% mass fraction of solute was evaporated off mg of water and then recovered to the original temperature. At t.degree. C., the solution of NaOH with a mass fraction of solute was evaporated off mg of water and recovered to the original temperature, and the saturated solution of NaOH with a mass fraction of 2a, and the mass of the original solution was obtained At t°C, the NaOH solution with a% mass fraction of solute is evaporated off mg of water and then recovered to the original temperature. At t.degree. C., the solution of NaOH with a mass fraction of solute was evaporated off mg of water and recovered to the original temperature, and the saturated solution of NaOH with a mass fraction of 2a, and the mass of the original solution was obtained

At t°C, the NaOH solution with a% mass fraction of solute was evaporated off mg of water and then recovered to the original temperature. At t.degree. C., the solution of NaOH with a mass fraction of solute was evaporated off mg of water and recovered to the original temperature, and the saturated solution of NaOH with a mass fraction of 2a, and the mass of the original solution was obtained At t°C, the NaOH solution with a% mass fraction of solute is evaporated off mg of water and then recovered to the original temperature. At t.degree. C., the solution of NaOH with a mass fraction of solute was evaporated off mg of water and recovered to the original temperature, and the saturated solution of NaOH with a mass fraction of 2a, and the mass of the original solution was obtained

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After evaporation of mg water from the NaOH solution having a mass fraction of solute, the solution becomes a NaOH unsaturated solution Vml having a mass fraction of solute of 2 a,... The mass concentration of the resulting solution is?

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