Question

How do you solve `abs(-3r)=9`?

Answer 1

`r=3`

Explanation:

Those bars around the `-3r` are called absolute value bars and they turn everything inside positive, after they are in base form that is:
Ex: `|3-10|=x` ; `|-7|=x`; `x=7`
For this problem the `-3r` is going to get turned positive:
`|-3r|=9` ; `3r=9`
Than divide the `3`:
`r=3`

Answer 2

`r=-3,3`

Explanation:

When you have an absolute value like this, you can set `-3r=9` and `-3r=-9`.

Solve both equations by dividing both sides by -3 and get `r=-3,3`.

If you want to check, try plugging -3 and 3 back into the original equation `abs(-3r)=9`.
It works out: `abs(-3(-3))=9` and `abs(-3(3))=9`.