(a) The cubic equation \(x^3+ax^2+bx-40=0\) has three positive integer roots. Two of the roots are \(2\) and \(4\). Find the other root and the value of each of the integers \(a\) and \(b\).

(b) Do not use a calculator in this question. Solve

\(x^3-5x^2-46x-40=0,\)

given that it has three integer roots, only one of which is positive.