Question

How do you solve `4 < 13 +r`?

Answer 1

Subtract `13` from both sides to get:

`-9 < r`

That is `r > -9`

In general, you can perform any of the following operations on an inequality and preserve its truth:

(1) Add or subtract a value on both sides.
(2) Multiply or divide by a positive value on both sides.
(3) Multiply or divide by a negative value on both sides and reverse the inequality (`<` becomes `>`, `>=` becomes `<=`, etc).