First, what I like to do is to deal with improper fractions. So I'm going to change 4 3/5 to 23/5.
5/6r = 23/5
Now all you have to do is to divide both sides by 5/6, because you want the r variable by itself. You can divide fractions just by inverting and multiplying.
5/6r • 6/5 = 23/5 • 6/5
r = 138/25
However, that is an improper fraction, so I'll change it back into a mixed number for you!
r = 5 13/25