Bronson collects a total of 12 + 13 = 25 oak leaves.
x% of the leaves are brown, which means x/100 * 25 = (25x)/100 = (1/4)x leaves are brown.
20% of the leaves are green, which means 20/100 * 25 = (1/5) * 25 = 5 leaves are green.
The rest of the leaves are yellow, which means the number of yellow leaves is 25 - [(1/4)x + 5].
We are given that the number of yellow leaves is 15, so we can write: 25 - [(1/4)x + 5] = 15.
Simplifying, we get: 25 - (1/4)x - 5 = 15.
Combining like terms, we get: 25 - 5 - 15 = (1/4)x.
Simplifying further, we get: 5 = (1/4)x.
Multiplying both sides by 4, we get: 20 = x.
The value of x is 20.
#### 20
The answer is: 20
Below is a math problem. Provide a detailed, step-by-step solution.

### Problem:
Bronson decides to collect Oak Leaves from around his Neighborhood. He collects 12 on Thursday and 13 on Friday. x% are Brown and 20% are Green. The rest are yellow. How many yellow leaves does he collect?
If we know the answer to the above question is 15, what is the value of unknown variable x?

### Answer:
