Jeff makes 10 donuts each day for 12 days, which means he makes a total of 10 * 12 = 120 donuts.
Jeff eats one of the donuts each day, so he eats a total of 12 donuts.
After Jeff eats his donuts, there are 120 - 12 = 108 donuts remaining.
Then, Chris comes over and eats x donuts.
The number of donuts remaining after Chris eats is 108 - x.
We are given that each box can fit 10 donuts, so the number of boxes Jeff can fill is (108 - x) / 10.
We are given that the number of boxes Jeff can fill is 10, so we can write: (108 - x) / 10 = 10.
Multiplying both sides by 10, we get: 108 - x = 100.
Solving for x, 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:
Jeff makes 10 donuts each day for 12 days. Jeff eats one of the donuts each day. Chris then comes over and eats x donuts. If 10 donuts fit in each box, how many boxes can Jeff fill with his donuts?
If we know the answer to the above question is 10, what is the value of unknown variable x?

### Answer:
