Answer: 6
Step-by-step explanation: We are told that the large cistern is completely filled shown with the larger volume. To find volume, the formula is lxwxh and if you apply that to the model, the larger cistern has a volume of 24 ft cubed which means 24 is completely filled. If we calculate the volume of the smaller cistern, it is 6. The question asks us how many cubic feet will be left when the larger cistern pours enough water to completely fill up the smaller cistern (24). So we do subtraction, 24-6= 18 meaning 18 is the number that is going to get poured from the big to the small cistern to make it 24 or, completely filled. And when we subtract the 18 from 24 (because we poured 18 from the large one to the small one to make it full), we get 6. 6 is how much is left after the larger cistern poured 18 to fill up the smaller cistern.