Question 23019
Use d=rt in he form t=d/r
Let the current speed be represented by "c".
Upstream Data:
d=36; rate= 15-c; therefore time upstream = 36/(15-c)
Downstream Data:
d=36; rate = 15+c; therefore time downstream = 36/(15+c)
EQUATION:
  Time up + Time down = 5 hrs
    36/(15-c) + 36/(15+c) = 5
     1/(15-c) + 1/(15+c) = 5/36
     30/(225-c^2) = 5/36
      6/(225-c^2) = 1/36
     6(36) = 225-c^2
    -c^2 = -9
      c = 3 mph (speed of current)

Cheers,
Stan H.