Theo drinks x cups of water every day.
Mason drinks 7 cups of water every day.
Roxy drinks 9 cups of water every day.
In one week, Theo drinks 7x cups of water (since there are 7 days in a week).
In one week, Mason drinks 7 cups of water every day, so he drinks a total of 7 * 7 = 49 cups of water.
In one week, Roxy drinks 9 cups of water every day, so she drinks a total of 9 * 7 = 63 cups of water.
The total number of cups of water the siblings drink together in one week is: 7x + 49 + 63.
We are given that the total number of cups of water is 168, so we can write: 7x + 49 + 63 = 168.
Simplifying the left side, we get: 7x + 112 = 168.
Subtracting 112 from both sides, we get: 7x = 56.
Dividing both sides by 7, we get: x = 8.
The value of x is 8.
#### 8
The answer is: 8
Below is a math problem. Provide a detailed, step-by-step solution.

### Problem:
Theo, Mason, and Roxy are siblings.  Theo drinks x cups of water every day. Mason drinks 7 cups of water.  Roxy drinks 9 cups of water every day.  In one week, how many cups of water do the siblings drink together?
If we know the answer to the above question is 168, what is the value of unknown variable x?

### Answer:
