Answer: The correct option is
(E) 80,000.
Step-by-step explanation: Given that after adding 4,000 gallons of water to a large tank that was already filled to [tex]\dfrac{3}{4}[/tex] of its capacity, the tank was then at [tex]\drac{4}{5}[/tex] of its capacity.
We are to find the number of gallons of water that the tank hold when filled to capacity.
Let the tank can hold x gallons of water when filled to capacity.
Then, according to the given information, we have
[tex]\dfrac{3}{4}x+4000=\dfrac{4}{5}x\\\\\\\Rightarrow \dfrac{4}{5}x-\dfrac{3}{4}x=4000\\\\\\\Rightarrow \dfrac{16-15}{20}x=4000\\\\\Rightarrow x=4000\times20\\\\\Rightarrow x=80000.[/tex]
Thus, the required capacity of the tank is 80,000 gallons of water.
Option (E) is CORRECT.