The speed of current is 8 km/h. A motorboat goes 150 km upstream and back again to the starting point in 11 hours 40 minutes.  The speed in (km/h) of motorboat and time it takes to travel 700 km in still water is?

28 km/h, 25 hours

11 hours 40 minutes = 11 + \(\frac{2}{3}\) hour

\(\frac{150}{x + 8}\) + \(\frac{150}{x - 8}\) = \(\frac{35}{3}\)

450 (x - 8) + 450 (x + 8) = 35x² - 35 × 64

900x = 35x² - 35 × 64

x = 28 km/h

time = \(\frac{700}{28}\) = \(\frac{100}{4}\) = 25 hours