Answer:The total amount of water in the aquarium is 42 7/20 gallons.
Explanations:From the question given, the initial gallons of water that Bill has is 23 3/4. If he adds 18 3/5 more gallons to it, the amount of water in his aquarium is expressed as:

Convert to improper fraction

Find the LCM:

Convert the result back to mixed fraction:

This shows that the total amount of water in the aquarium is 42 7/20 gallons.