dear friend, check the question you have typed, seems to be a typo, cause assuming -t2 in

V = (-t2 + 12t + 24)Ï€ m3

is -(t)^2 and also

1/3d

is d/3, i get the height as 62/9 m which is not the option. here goes the solution:-

Volume of a cylinder is pie r^2 h = 9 x pie x h

from V@4 = (-(4)^2 + 12x4 +24)pie = 56 pie or 9 x pie x (56/9) => h - 56/9 = d --- (1)
from V@6 = (-(6)^2 + 12x6 +24)pie = 60 pie or 9 x pie x (60/9) => h - 60/9 = d/3 --- (2)

from (1) and (2) you get d = 2/3 and hence h = 62/9

pls do check and confirm

Sorry typo error. Please read that as t square.