The hardness of `10^5` L of a sample of `H_2O` was completely removed by passing through a zeolite softener. The bed on exhaustion required 500 L of NaCl solution containing `15gL^(-1)` of `NaCl` for regeneration. Calculate the hardness of the sample of water.

Explanation

To calculate the hardness of the water sample, we will follow these steps:

### Step 1: Calculate the total mass of NaCl used for regeneration
Given that the NaCl solution has a concentration of 15 g/L and a total volume of 500 L, we can calculate the total mass of NaCl used.

\[ \text{Total mass of NaCl} = \text{Concentration} \times \text{Volume} \]
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