Step 1: Use the concept of equal distances.
\[
\sqrt{(x - 3)^2 + (y - 6)^2} = \sqrt{(x + 3)^2 + (y - 4)^2}
\]
Step 2: Square both sides.
\[
(x - 3)^2 + (y - 6)^2 = (x + 3)^2 + (y - 4)^2
\]
Step 3: Expand and simplify.
\[
x^2 - 6x + 9 + y^2 - 12y + 36 = x^2 + 6x + 9 + y^2 - 8y + 16
\]
Cancel \( x^2, y^2, 9 \):
\[
-6x - 12y + 36 = 6x - 8y + 16
\]
\[
-12x - 4y + 20 = 0
\]
\[
3x + y - 5 = 0
\]
Step 4: Final Relation.
\[
\boxed{3x + y - 5 = 0}
\]