Question 336593
Going upstreams slows the boat; going downstream will speed up the boat.

Boat Upstream:

rate = x - 12

time = 6 

Boat Downstream:

rate = x + 8

time = 5

Distances are equal.

Let x = speed of the boat in still water


6(x - 12) = 5(x + 8)

6x - 72 = 5x + 40

6x - 5x = 72 + 40

x = 112 km per hour.