3|3 - 5r| - 3 = 18

Isolate the absolute value term:

    3|3 - 5r| = 21

Divide both sides by 3

     |3 - 5r| = 7

Since bot |7| = 7 and |-7| = 7, what's between
the absolute value bars 3-5r could equal to 7 or -7.
So we make two equations:

    3 - 5r = 7           3 - 5r = -7
       -5r = 4              -5r = -10
         r =               r = 2

Edwin