Cost of bottles that come in packs of 12 = 3 dollars
It is already given in the question that i drink 3 bottles per day. So the cost of 3 bottles has to be determined first and then the number of bottles that is drunk in a week also has to be determined. after that the cost per week can be easily determined.
Number of bottles drunk per day = 3
So
The number of bottles drunk in a week = (3 * 7) bottles
= 21
Now
Cost of a pack of 12 bottles = 3 dollars
Then
Cost of 1 bottle = (3/12) dollars
= (1/4) dollars
= 0.25 dollars
So
The cost of 21 bottles = (21 * 0.25) dollars
= 5.25 dollars
So the cost per week as determined above is $5.25.
