The answer is A. Let me know if you need an explanation.
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:

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:
3. Now, you can write the result in Scientific notation, as following:

The answer is: 
A because radius is half of the diameter
Minus p both sides
xy=5-p
divide both sides by x
y=(5-p)/x
B