Since the rate = distance/time
Since the distance is 128 km
Since the time of upstream is 4 hours
Then the rate of the boat in the still water is
[tex]\begin{gathered} R_s=\frac{128}{4} \\ R_s=32km\text{ per hour} \end{gathered}[/tex]Since the boat took 2 hours downstream, then
The rate of the current is
[tex]\begin{gathered} R_c=\frac{128}{2} \\ R_c=64km\text{ per hour} \end{gathered}[/tex]