Number of brown trout = 6
Number of lake trout = 18
Total number of trouts = 
Probability to catch a lake trout first time = 
As the fisherman let the trout go, so probability for the second time is =

Hence, the probability becomes=

= 
The probability to find the brown trout is 
as , 
= 
Answer: 30515 meters
Explanation: Since there are 1000 m in a kilometer we multiply 30.515 by 1000 to get 30515
0.57 = 57/100 this means it has to be rational. :D hope I helped :)