Well, after working the problem I came up with 50625 ft-lb. Wrong. Ugh.
I tried using a linear relationship. y=12/5y+12
dV=108/5*y + 108
I multiplied by the density of water(62.5 lb/ft^3). d=m/v then d*v=m.
Now I integrate from zero to five.
[675x^2+6750x](zero to five)=50625 ft-lb...