find the speed of the boat in still water

Question

A boat travels down a river. It takes 120 minutes to travel the outward journey that is made following the current of the river. On the way back, with the current against him, he spends three hours. Knowing that the current of the river is 8 km/h, find the speed of the boat in still water

Answer 1

2 hours upstream, 3 hours downstream

current speed = c = 8 km/hr

boat speed = b

distance = time times speed

d=rt

d = 2(b+c) = 3(b-c)

2b +2c = d

3b-3c = d

b+c = d/2

b+8 =d/2

b-c = d/3

b-8 = d/3

b+8 = d/2

b-8 = d/3

subtract

16 = d/2 -d/3 = d/6

d= 6(16) = 96 kilometers

b+8 = 96/2 = 48

b = 48-8 = 40 km/hr

40+8 = 48 down stream = 96/48= 2 hours

40-8= 32 upstream = 96/32 = 3 hours

the boat went 40 kilometers per hour in still water

Answer 2

d_out = 2(s + 8)

d_back = 3(s - 8)

2(s + 8) = 2(s -8)

Can you solve for s and answer?