A boat crosses a river from one bank A to another bank B which is opposite. The distance between them is D. The speed of water is \(V_W\) and that of boat relative to water is \(V_B\). If \(V_B = 2V_W\), the time taken by the boat to cross the river directly along AB is \((sin30^{\circ} = \frac{1}{2})\), \((cos30^{\circ} = \frac{\sqrt{3}}{2})\)