This is solving inequalites
When you are working with an equation involving inequalities (<,>) you can treat it just like an equation with an = sign. So we can use the same rules, and we will be trying to get the r "by itself". In order to do this we have to do the opposite of whatever is happening to r to both sides of our equation.
Currently we are subtracting 9 from the r side of the equation, so we will add 9 to each side giving us,
Now we are multiplying r by 4, so we will divide both sides by 4. This gives us,
I hope this helps!