`NaCl` of `95%` purity is used to prepare salt cake `(Na_(2)SO_(4))` by the reaction,
`2NaCl+H_(2)SO_(4)rarrNa_(2)SO_(4)+2HCl.`
If the product `(Na_(2)SO_(4))` is only `85%` pure, what weight of `NaCl` is used up in producing 1 kg of the impure salt cake ?

Explanation

To solve the problem, we need to determine the weight of NaCl used to produce 1 kg of impure Na2SO4, given that NaCl has a purity of 95% and the Na2SO4 produced is only 85% pure.

### Step-by-Step Solution:

1. **Define Variables**:
Let \( x \) be the weight of NaCl used in grams.

2. **Calculate the Mass of Pure NaCl**:
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