Can I get some help, please, I'm so confused. Thx!

Answer:
13.89 ft³
Step-by-step explanation:
The volume of a rect. prism is BxWxH. since you're looking for unfilled it's a little but tricky-er.
You know that the tank already has 1/3 ft deep water, so you take 1/3 off the height.
now you have
5 x 1 2/3 x 1 2/3
8 1/3 x 1 2/3
13 8/9 or 13.888888 or ~13.89
so
13.89 ft³
I also haven't done a problem like that in 1-2 years so tell me if I got it wrong