Add:
`a + b - 3, b - a + 3, a - b + 3`

Answer

To solve the problem of adding the expressions \( a + b - 3 \), \( b - a + 3 \), and \( a - b + 3 \), we will follow these steps:

### Step 1: Write down the expressions
We have the following expressions to add:
1. \( a + b - 3 \)
2. \( b - a + 3 \)
3. \( a - b + 3 \)

### Step 2: Combine the expressions
We can combine these expressions into one equation:
\[ (a + b - 3) + (b - a + 3) + (a - b + 3) \]

### Step 3: Remove the brackets
Since we are adding all the expressions, we can remove the brackets without changing the signs:
\[ a + b - 3 + b - a + 3 + a - b + 3 \]

### Step 4: Group like terms
Now, we will group the like terms together:
- The \( a \) terms: \( a - a + a \)
- The \( b \) terms: \( b + b - b \)
- The constant terms: \( -3 + 3 + 3 \)

### Step 5: Simplify each group
1. For the \( a \) terms:
\[ a - a + a = a \]
2. For the \( b \) terms:
\[ b + b - b = b \]
3. For the constant terms:
\[ -3 + 3 + 3 = 3 - 3 + 3 = 3 \]

### Step 6: Combine the results
Now, we combine the simplified terms:
\[ a + b + 3 \]

### Final Answer
Thus, the final result of adding the three expressions is:
\[ \boxed{a + b + 3} \]