Question

How do you solve `9=7z-13z-21`?

Answer 1

`z=-5`

Explanation:

You combine `7z` and `-13z` to get `-6z`, so

`9=-6z-21`

Add `21` to both sides

`30=-6z`

Divide both sides by `-6`

`-5=z`

Answer 2

`z = -5`

Explanation:

When solving equations, we can combine like terms as shown below:

`5x + 4x -> 9x`

So to solve this problem, we need to isolate the variable "`z`"
We do this by combining all terms with the variable `z` on them.

`9 = 7z - 13z - 21`

`9 = -6z - 21`

Then we treat it as a regular algebra problem by isolating the variable

`9 = -6z - 21`

`30 = -6z`

`z = -5`

Note: Combining like terms can only be done with variables of the same degree, or in other words, variables raised to the same exponent. Example below:

`5z + 3z^2` cannot be combined into one expression, but

`3z^2 + 5z^2` can be combined to produce `8z^2`