We are given that the point \( (x, y) \) is equidistant from the points \( (3, 6) \) and \( (-3, 4) \).
To find the relation, we use the distance formula. The distance between two points \( (x_1, y_1) \) and \( (x_2, y_2) \) is given by:
\[
d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}
\]
First, find the distance from \( (x, y) \) to \( (3, 6) \):
\[
d_1 = \sqrt{(x - 3)^2 + (y - 6)^2}
\]
Next, find the distance from \( (x, y) \) to \( (-3, 4) \):
\[
d_2 = \sqrt{(x + 3)^2 + (y - 4)^2}
\]
Since the point \( (x, y) \) is equidistant from both points, we set \( d_1 = d_2 \):
\[
\sqrt{(x - 3)^2 + (y - 6)^2} = \sqrt{(x + 3)^2 + (y - 4)^2}
\]
Now, square both sides to eliminate the square roots:
\[
(x - 3)^2 + (y - 6)^2 = (x + 3)^2 + (y - 4)^2
\]
Expand both sides:
\[
(x^2 - 6x + 9) + (y^2 - 12y + 36) = (x^2 + 6x + 9) + (y^2 - 8y + 16)
\]
Simplify:
\[
x^2 - 6x + 9 + y^2 - 12y + 36 = x^2 + 6x + 9 + y^2 - 8y + 16
\]
Cancel the common terms \( x^2 \) and \( y^2 \) from both sides:
\[
-6x + 9 + 36 - 12y = 6x + 9 - 8y + 16
\]
Simplify further:
\[
-6x + 45 - 12y = 6x + 25 - 8y
\]
Now, move all the terms involving \( x \) and \( y \) to one side:
\[
-6x - 6x + 45 - 12y + 8y = 25
\]
Simplify:
\[
-12x - 4y + 45 = 25
\]
Move the constants to the other side:
\[
-12x - 4y = -20
\]
Finally, divide through by -4:
\[
3x + y = 5
\]
Conclusion:
The relation between \( x \) and \( y \) is:
\[
\boxed{3x + y = 5}
\]