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A boat's crew rowed 12 miles downstream, with the current, in 1.5 hours. The return trip upstream, against the current covered the same distance, but took 4 hours. Find the crew's rowing rate in still water and the rate of the current...

The crew's rowing rate in still water is ??? mile(s) per hours.
The rate of the currents is ??? mile(s) per hour.

Please HELP, this question is hard, and I don't understand it.

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  1. Let the rowing rate be x mph
    let the current's rate by y mph

    going with the current, will be a rate of x+y mph
    going against the current would be x-y mph

    so you get two equations, using Distance = rate x time

    1.5(x+y) = 12
    4(x-y) = 12

    1st: divide by 1.5
    ---> x+y = 8
    2nd: divide by 4
    ---> x-y = 3

    add them
    2x = 11
    x = 5.5 mph
    back in 1st, y = 2.5 mph

    so the rowing speed is 5.5 mph,
    the current's speed is 2.5 mph

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