Question

How do you solve `r + 8.2 + 0.4r = -8.6`?

Answer 1

`r=-12`

Explanation:

To simplify I would suggest multiplying everything by `10` to clear the decimal fractions.
`color(white)("XXX")10r+82+4r=-86`

Subtract `82` from both sides, isolating the `r` factors on one side and the constant s on the other.
`color(white)("XXX")10r+4r=-86-82`

Combine terms on both sides.
`color(white)("XXX")14r = -168`

Divide both sides by `14`
`color(white)("XXX")r=-12`