A boat takes total 8 hrs. to cover a distance of 64 km in upstream and 80 km in downstream. While it takes 8.5 hrs. to cover a distance of 80 km in upstream and 70 km in downstream. Find speed of the boat.

18 km/hr

\(\frac{64}{x - y}\) + \(\frac{80}{x + y}\) = 8   ---(i)

\(\frac{8}{x - y}\) + \(\frac{10}{x + y}\) = 1   ---(i)

\(\frac{80}{x - y}\) + \(\frac{70}{x + y}\) = 8.5   ---(ii)

(i) x 10 - (ii) x 1 

\(\frac{30}{x + y}\) = 1.5

x + y = 20

x - y = 16

x = 18, y = 2