Mishka's speed = 14 km/hr
Current speed = 2 km/hr
Explanation:
Let the speed of rowing be r and speed of current be c.
If he rows with the current, Mishka rows 48 km in 3 hours.
Relative speed = r + c
Distance = 48 km
Time = 3 hours
48 = 3 x ( r+c)
r + c = 16 ---------------------------eqn 1
If he rows against the current, it takes 4 hours to travel the same distance.
Relative speed = r - c
Distance = 48 km
Time = 4 hours
48 = 4 x ( r - c)
r - c = 12 ---------------------------eqn 2
eqn 1 + eqn 2
2r = 28
r = 14 km/hr
Substituting in eqn 1
14 + c = 16
c = 2 km/hr
Mishka's speed = 14 km/hr
Current speed = 2 km/hr