I'm gonna do this 2 ways because I'm not sure what you mean about the line. I'm going to indicate greater than or equal to with >=.
1st I'll solve for
r/15 >= -3
multiply by 15 on each side
r >= -45
Next I'll solve for
r/15 >= 3
multiply 15 on each side
r >= 45
So depending on if that is a 3 or -3 that is how you would do it....
So did I read the problem right?