Question 79166
distance=rate*time.
9=(r-6)t upstream
16=(r+6)t downstream.
seeing as the times are equal we have:
9/(r-6)=16/(r+6)
16r-96=9r+54
16r-9r=54+96
7r=150
r=21.43 kl/h speed of the boat in still water. 
proof
9/(21.43-6)=16/(21.43+6)
9/15.43=16/27.43
.5833=.5833