You should come up with the notation for the speed of the boat such that: x miles/hour.
The speed of the boat upstream is x - 20 (the speed of boat in steel water).
The speed of the boat downstream is x + 20.
The problem provide the information that the boat travels 60 miles downstream in the same time it travels 40 miles upstream such that:
`60/(x+20) = 40/(x-20)`
`40(x+20) = 60(x-20)`
`2(x+20) = 3(x-20)`
You need to open brackets such that:
`2x + 40 = 3x - 60`
You need to move the terms that contains x to the left side such that:
`2x - 3x = -60 - 40`
`-x = -100 =gt x = 100`
Hence, evaluating the speed of the current under given conditions yields `x = 100` miles/hour.