Answer:
The value is

Step-by-step explanation:
From the question we are told that
The volume of the drinking water is
The mass of mercury it contains

Generally the mass of water is mathematically represented as
Here
is the density of water with value

So
=>
Generally ppb mean part per billon , and 1 billon is 100,000,000
So the part per billon which this represents is mathematically represented as

=>
