A boat traveled 36 mi up a river in 3 hours, returning downstream, the boat took 2 hours. What is the boat's rate in still water and what is the rate of the river's current?

Answer 1

(Vb-Vr) * T1 = 36
(Vb-Vr)3 = 36
Eq1: Vb - Vr = 12

(Vb+Vr) * T2 = 36
(Vb+Vr)2 = 36
Eq2: Vb + Vr = 18
Add Eq1 and Eq2:

Vb - Vr = 12.
Vb + Vr = 18.
Sum: 2Vb = 30, Vb = 15 mi/h.

In Eq1, replace Vb with 15:
15 - Vr = 12, Vr = 3 mi/h.