(a) Express \(3 \cos x + 2 \cos(x - 60^\circ)\) in the form \(R \cos(x - \alpha)\), where \(R > 0\) and \(0^\circ < \alpha < 90^\circ\). State the exact value of \(R\) and give \(\alpha\) correct to 2 decimal places.

(b) Hence solve the equation \(3 \cos 2\theta + 2 \cos(2\theta - 60^\circ) = 2.5\) for \(0^\circ < \theta < 180^\circ\).