SOLUTION: Crystal rows a boat downstream for 90 miles. The return trip upstream took 8 hours longer. If the current flows at 2 mph, how fast does Crystal row in still water?

Time equation is


     -  = 8 hours.


where x is the value under the question.


    90*(x+2) - 90*(x-2) = 8*(x^2-4)

    90x + 180 - 90x + 180 = 8x^2 - 32

    8x^2 = 360 + 32 = 392

     x^2 = 392/8 = 49

     x           =  = 7.


ANSWER.  The rate of the boat in still water is 7 miles per hour.