Final answer:
The amount of water in the two tanks will be the same after 72 weeks.
Step-by-step explanation:
To find out after how many weeks the amount of water in the two tanks will be the same, you can set up an equation to represent the situation. Let x be the number of weeks.
For the first tank, the amount of water remaining after x weeks can be represented as 648 - 4x.
For the second tank, the amount of water remaining after x weeks can be represented as 864 - 7x.
Setting these two expressions equal to each other, we get:
648 - 4x = 864 - 7x
Solving for x, we subtract 648 from both sides and add 7x to both sides:
216 = 3x
x = 72
Therefore, the amount of water in the two tanks will be the same after 72 weeks.