5. The circle \(C\) has centre \(( 3,1 )\) and passes through the point \(P ( 8,3 )\).
- Find an equation for \(C\).
- Find an equation for the tangent to \(C\) at \(P\), giving your answer in the form \(a x + b y + c = 0\), where \(a , b\) and \(c\) are integers.