Step-by-step explanation:
D = rate x time
D = (rate of current + rate of boat) x time
168 = (y - x) t against the current trip upstreams
168 = (y + x) t with the current trip downstream
168 = (y - x) 4
168 = (y + x) 3.5
since 168 = 168, we can set the equations equal to each other:
(y - x)4 = (y+x)3.5
4y - 4x = 3.5y +3.5x
4y - 3.5y = 3.5x + 4x
0.5y = 7.5x
y =15x
the rate of the current is 15 times the rate of the boat.
168 =4(15x) - 4x
168 = 60x - 4x
168 = 56x
x = 3
y = 15x
y = 15(3)
y = 45
