Add:
`ab - 4a, 4b - ab, 4a - 4b`

Answer

To solve the problem of adding the expressions \( ab - 4a \), \( 4b - ab \), and \( 4a - 4b \), we will follow these steps:

### Step 1: Write down the expressions
We start with the three expressions:
1. \( ab - 4a \)
2. \( 4b - ab \)
3. \( 4a - 4b \)

### Step 2: Combine the expressions
Now, we will add them together:
\[ (ab - 4a) + (4b - ab) + (4a - 4b) \]

### Step 3: Rearrange the terms
Next, we can rearrange the terms to group like terms together:
\[ (ab - ab) + (-4a + 4a) + (4b - 4b) \]

### Step 4: Simplify each group
Now, we simplify each group:
- \( ab - ab = 0 \)
- \( -4a + 4a = 0 \)
- \( 4b - 4b = 0 \)

### Step 5: Combine the results
Putting it all together, we have:
\[ 0 + 0 + 0 = 0 \]

### Final Answer
The sum of the expressions \( ab - 4a \), \( 4b - ab \), and \( 4a - 4b \) is:
\[ \boxed{0} \]

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