The point \(A\) has coordinates \((4, 6)\).
Given that \(OA\), where \(O\) is the origin, is a diameter of circle \(C\),
- find an equation for \(C\). [4]
Circle \(C\) crosses the \(x\)-axis at \(O\) and at the point \(B\).
\begin{enumerate}[label=(\roman*)]
\setcounter{enumi}{1}
\item Find the coordinates of \(B\). [2]
\item Find an equation for the tangent to \(C\) at \(B\), giving your answer in the form \(ax + by = c\), where \(a\), \(b\) and \(c\) are integers. [5]