Given
The cost of 5 bottles of water is 7.50 dollar.
Step-by-step explanation
To determine the cost of one dozen bottles of water.
1 dozen=12
From the unitary method,
5 bottle cost is 7.50 dollar.
1 bottle cost is

12 bottle costs is

Answer
Hence the cost of one dozen bottle of water is 18 dollar.
The correct option is C.