divide and simplify r^2+9r/r^2+5r-36/r/+4
not quite sure what you have written, but you can cancel factors if you rewrite
r^2+9r = r(r+9)
r^2+5r-36 = (r-4)(r+9)
so the first part reduces to r/(r+4)
r^2+9r = r(r+9)
r^2+5r-36 = (r-4)(r+9)
so the first part reduces to r/(r+4)