Question 372132
Downstream time is 60/(15 + c) Upstream time is 60/(15 - c)
Equation is therefore 3x60/(15 + c) = 2x 60/(15 - c)
So 180 (15 - c) = 120(15 + c)
2700 - 180c = 1800 + 120c
900 = 300c
c = 3
Check : Downstream at 18 mph takes 10/3 hours
Upstream at 12 mph takes 5 or 15/3 hours
Ratio is 3:2