4 The complex numbers \(a\) and \(b\) are given by \(a = 7 + 6 \mathrm { i }\) and \(b = 1 - 3 \mathrm { i }\). Showing clearly how you obtain your answers, find
\(| a - 2 b |\) and \(\arg ( a - 2 b )\),
\(\frac { b } { a }\), giving your answer in the form \(x + \mathrm { i } y\).