How do you find perimeter in general? You add up all the sides. So, let's do that. 2r+5+2r+4r-3+r= 6r+2. So, the perimeter is equal to 6r+2. But wait it is also equal to 38 (it is in the question). So, if both are the perimeter, they are the same. So, set them equal to each other.
6r+2=38
6r=36
r=6
