Add the following expressions:
`2x+9y-7z, 3y+z-3x, 3z-4y-x`

Answer

To add the expressions \(2x + 9y - 7z\), \(3y + z - 3x\), and \(3z - 4y - x\), we can follow these steps:

### Step 1: Write down all the expressions together
We start by writing the expressions in one line:
\[ 2x + 9y - 7z + 3y + z - 3x + 3z - 4y - x \]

### Step 2: Rearrange the expression
Next, we can rearrange the expression by grouping like terms together:
\[ (2x - 3x - x) + (9y + 3y - 4y) + (-7z + z + 3z) \]

### Step 3: Combine the like terms for \(x\)
Now, we combine the coefficients of \(x\):
\[ 2 - 3 - 1 = -2 \]
So, the term for \(x\) becomes:
\[ -2x \]

### Step 4: Combine the like terms for \(y\)
Next, we combine the coefficients of \(y\):
\[ 9 + 3 - 4 = 8 \]
So, the term for \(y\) becomes:
\[ 8y \]

### Step 5: Combine the like terms for \(z\)
Finally, we combine the coefficients of \(z\):
\[ -7 + 1 + 3 = -3 \]
So, the term for \(z\) becomes:
\[ -3z \]

### Step 6: Write the final expression
Putting it all together, we have:
\[ -2x + 8y - 3z \]

### Final Answer:
The sum of the given expressions is:
\[ -2x + 8y - 3z \]

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