Simplify the following expression by combining like terms:
`3\left(x+y\right)+2z-5x-3x-7y`
To simplify the expression `3(x+y) + 2z - 5x - 3x - 7y`, we can combine like terms.
First, let's distribute the 3 to terms inside the parentheses:
`3x + 3y + 2z - 5x - 3x - 7y`
Next, let's group the like terms together:
`(3x - 5x - 3x) + (3y - 7y) + 2z`
Now, we can simplify the like terms within each group:
`(-5x - 3x + 3x) + (-7y + 3y) + 2z`
Combining like terms within each group gives us:
`-5x - 7y + 2z`
So the simplified expression is `-5x - 7y + 2z`.