The boy squirrel gathers 6 walnuts and carries them to the burrow, adding to the 12 already there, so the total number of walnuts in the burrow is 6 + 12 = 18.
On the way to the burrow, the boy squirrel drops x walnuts, so the total number of walnuts in the burrow is now 18 - x.
The girl squirrel brings 5 more walnuts to the burrow, making the total number of walnuts in the burrow 18 - x + 5 = 23 - x.
The girl squirrel eats 2 walnuts, so the total number of walnuts left in the burrow is 23 - x - 2 = 21 - x.
We are given that the total number of walnuts left in the burrow is 20, so we can write: 21 - x = 20.
Solving for x, we get: x = 1.
The value of x is 1.
#### 1
The answer is: 1
Below is a math problem. Provide a detailed, step-by-step solution.

### Problem:
A boy squirrel gathers 6 walnuts and carries them to his burrow in the tree, adding to the 12 already there, and dropping x on the way. The girl squirrel brings 5 more walnuts to their burrow and eats 2.  How many walnuts are left?
If we know the answer to the above question is 20, what is the value of unknown variable x?

### Answer:
