Part of work done in two hours = \( \Large \frac{1}{4}+\frac{1}{6}=\frac{5}{12} \) Part of work done in 4 hours = \( \Large 2 \left(\frac{5}{12}\right) = \frac{5}{6} \) Therefore, required time = \( \Large 4 + \frac{\frac{1}{6}}{\frac{1}{4}} = 4\frac{2}{3} hours \)