The speed of the current is 4kph. A boat travels 6km upstream in the same time it takes to travel 10km downstream. What is the spees of the boat in still water?

Answer 1

d = (Vb-Vc)*T = 6km.
(Vb-4)T = 6.
Eq1: Vb*T - 4T = 6.

(Vb+Vc)*T = 10 km.
(Vb+4)*T = 10.
Eq2: Vb*T + 4T = 10.

Subtract the Eqs:
Vb*T - 4T = 6.
Vb*T + 4T = 10.
-8T = -4.
T = 0.5h.

In Eq1, replace T with 0.5h:
Vb*0.5 - 4*0.5 = 6.
0.5Vb = 8.
Vb = 16 km/h.