Step 1: Use the property of equal radii.
Since the circle passes through \((0,a)\) and \((b,h)\) and has centre \((c,0)\), the distances from the centre to these points are equal.
Thus,
\[
\sqrt{(0-c)^2+(a-0)^2}
=
\sqrt{(b-c)^2+h^2}
\]
Step 2: Square both sides.
\[
c^2+a^2
=
(b-c)^2+h^2
\]
Expanding,
\[
c^2+a^2
=
b^2-2bc+c^2+h^2
\]
Cancelling \(c^2\),
\[
a^2=b^2-2bc+h^2
\]
Step 3: Solve for \(c\).
\[
2bc=b^2-a^2+h^2
\]
Therefore,
\[
c=\frac{b^2-a^2+h^2}{2b}
\]
Step 4: Final conclusion.
Therefore,
\[
\boxed{\frac{b^2-a^2+h^2}{2b}}
\]