Finding the points of intersection

Find the points of intersection of the circles $x^2 + y^2 - 18x - 4y + 35 = 0$ and $x^2 + y^2 + 2x + 6y -15 = 0$ .

If your answer is $(a,b)$ and $(c,d)$ , give your answer as $a+b+c+d$ .