Find all $x$-intercepts of the graph of $x^2 - 2x + y^2 + 6y - 15 = 0$. Write your answer as a list of ordered pairs, separated by commas.

When we plot the graph of x^2 - 2x + y^2 + 6y - 15 = 0, we get a circle centered at (1,-3) with radius 2*sqrt(7).  Then by the Pythagorean Theorem, the x-intercepts are (-4,0) and (6,0).