Motor Velocity

Let the speed of motor boat be V_m
let the speed of stream be V_s
For the raft the motot boat downstream goes at a speed of
(V_m + V_s - V_s) = V_m
for upstream = { V_m- V_s - (-V_s)} = V_m
Now since the displacement wrt to raft of the motor boat is zero, time for upstream journey is also 60min
{ since displcement is zero so V_m*60 - V_m*t = 0 so t is 60 Min)
now the speed of raft is same as speedfor the stream
so V_s* ( 60 + 60 )= 6 km
solving we get V_s= 3 km/mi
please check the ans whether it is right or not

Let speed of raft(stream) be u km/hr
and speed of motorboat wrt water be v km/hr
v_MR=v+u
v_RaftR=u

In 1 hr, dist. covered by M = v+u km
In 1 hr, dist. covered by Raft = u km
Extra distance covered by motorboat = v km

let after time t they meet,
ut=t(v-u)
or 2u = v [since V_MR when going upstream is -(v-u) (considering initial dirn positive]

Now, u(t+1) = 6 or ut + u = 6(1)
and (v+u) - (v-u)t = 6
or 3u - ut = 6 - (2)

Adding 1 and 2
4u = 12 or u = 3