Simplify :
`3x - [3x - {3x - (3x - bar(3x - y))}]`

Answer

To simplify the expression \( 3x - [3x - \{3x - (3x - \bar{(3x - y)})\}] \), we will follow the order of operations, also known as the BODMAS/BIDMAS rule (Brackets, Orders, Division and Multiplication, Addition and Subtraction). We will work from the innermost brackets to the outermost.

### Step-by-Step Solution:

1. **Identify the innermost expression**:
We start with the innermost expression: \( \bar{(3x - y)} \). The bar indicates that we are subtracting \( (3x - y) \) from \( 3x \).

2. **Simplify the innermost expression**:
\[ 3x - \bar{(3x - y)} = 3x - (3x - y) = 3x - 3x + y = y \]
Now, we replace \( \bar{(3x - y)} \) with \( y \).

3. **Substitute back into the expression**:
Now the expression becomes:
\[ 3x - [3x - \{3x - (y)\}] \]

4. **Simplify the next innermost expression**:
\[ 3x - (y) = 3x - y \]
Now, we replace \( 3x - (y) \) with \( 3x - y \).

5. **Substitute back into the expression**:
The expression now is:
\[ 3x - [3x - (3x - y)] \]

6. **Simplify the next bracket**:
\[ 3x - (3x - y) = 3x - 3x + y = y \]
Now, we replace \( 3x - (3x - y) \) with \( y \).

7. **Substitute back into the expression**:
The expression now is:
\[ 3x - [y] \]

8. **Final simplification**:
\[ 3x - y \]

### Final Answer:
The simplified expression is:
\[ 3x - y \]