First let's find the volume of the fish tank. Given that the dimensions are 60 by 15 by 34, then:
[tex]V=(60)(15)(34)=30600[/tex]we have that the total volume of the fish tank is 30600 u³. But we only want to know how much is 3/4 of the total volume, then:
[tex](30600)(\frac{3}{4})=22950[/tex]therefore, to fill three fourths of the aquarium we will need 22950 u³ of water