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Answer:
21.1%
Explanation:
Adding 402 g of salt to a solution whose volume is 130 × 100 mL will increase the concentration by (402/130)%, or about 3.09%.
When the concentration of 18% has 3.09% added to it, the concentration of the new mixture is about 21.1%.
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Additional comment
We understand the units of concentration used here to be (1 g)/(100 mL) = 1%. These units are often used for a solution with a dissolved solid.