x^2-6x+y^2-2y=18 is another way of writing this equation. This can be further modified:
x^2-6x+9 + y^2-2y+1=18+10; (x-3)^2+(y-1)^2=28 is of the form X^2+Y^2=a^2 which is the equation of a circle of radius a. In this case a=sqrt(28)=2sqrt(7). The centre of the circle is (3,1) found by setting X and Y to zero and solving for x and y. Therefore, k=3, l=1 and r=a=2sqrt(7).