Explanation of the solution to the problem: you must first draw up the reaction equation:
H3PO4 + 3NaOH = Na3PO4 + 3H2O
Next, we find the amount of sodium hydroxide substance, the amount of phosphoric acid substance is 1/3 the amount of sodium hydroxide substance (3 times less) = 0.6 mol, then we find the mass of phosphoric acid by multiplying the amount of substance by its molar mass. To find the mass of the solution, divide the resulting mass by the mass fraction.
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