Question 1201539

A boat takes 12 hours to cover (D+30) km in upstream
upstream speed = (d+30)/12

 and it takes 8 hours to cover D km in downstream.
downstream speed = d/8

stream speed = 4 km / h

downstream speed - upstream speed = 8 (2*4)

d/8  - (d+30)/12 =8

3d/24 - 2(d+30)/24 =8


(3d-2d-60)/24 =8

d-60 = 192

d= 252
Upstream speed = (252+30)/12 =23.5 km/h

d-64 = 252-64 = 188

188/23.5 = 8 hours to cover (D-64) km