Simplify combining like terms:
`3a - 2b - ab - (a - b + ab) + 3ab + b - a`

Answer

To simplify the expression `3a - 2b - ab - (a - b + ab) + 3ab + b - a`, we will follow these steps:

### Step 1: Remove the parentheses
The expression is:
\[ 3a - 2b - ab - (a - b + ab) + 3ab + b - a \]

When we remove the parentheses, we need to change the signs of the terms inside the parentheses because of the negative sign in front of it:
\[ 3a - 2b - ab - a + b - ab + 3ab + b - a \]

### Step 2: Combine like terms
Now we will group the like terms together. The like terms are those that have the same variable part.

- For the terms with \(a\):
- \(3a - a - a = 3a - 2a = a\)

- For the terms with \(b\):
- \(-2b + b + b = -2b + 2b = 0\)

- For the terms with \(ab\):
- \(-ab - ab + 3ab = -2ab + 3ab = ab\)

### Step 3: Write the simplified expression
Now we can combine all the simplified terms:
\[ a + 0 + ab = a + ab \]

Thus, the simplified expression is:
\[ a + ab \]

### Final Answer:
The simplified expression is:
\[ a + ab \]

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