1. The combined volume of all the tanks at the aquarium is written in Scientific notation. Keeping this on mind, you can write it as following:
[tex](1.25)(10^{6})=1,250,000gallons[/tex]
2. Now, you must sum the combined volume of all the tanks and the volume of the new tank to calculate the total volume of all of them:[tex]Vt=1,250,000gallons+250,000gallons\\Vt= 1,500,000gallons[/tex]
3. Now, you can write the result in Scientific notation, as following:
[tex]Vt=(1.5)(10^{6}) gallons[/tex]
The answer is: [tex](1.5)(10^{6}) gallons[/tex]