
To solve for r, the objective is to isolate the variable on one side of the equation and all other terms on the other side.
- First, pass "3" to the right side of the equation by applying the opposite operation "-3" to both sides of the equal sign:

-Second, pass "3r" to the left side of the equation by applying the opposite operation "-3r" to both sides of it:

Third, the variable is being multiplied by "-2", to cancel this multiplication you have to apply the opposite operation, that is, divide the term by -2. And to keep the equality valid, you have to divide both sides.

The result is r=4.