4 The points \(A , B\) and \(C\) have position vectors \(\binom { - 2 } { 1 } , \binom { 2 } { 5 }\) and \(\binom { 6 } { 3 }\) respectively. \(M\) is the midpoint of \(B C\).
- Find the position vector of the point \(D\) such that \(\overrightarrow { B C } = \overrightarrow { A D }\).
- Find the magnitude of \(\overrightarrow { A M }\).