Question 1171113
time to go upstream is 64/(8-c) km/km/h =h
time to go downstream is 64/(8+c)
64/(8-c)=3*64/(8+c) 
cross-multiply
512+64c=1536-192c 
256c=1024  
c=4 km/h

so it is 16 hours upstream and 5 1/3 hours downstream