Kellen​'s boat travels 15 mph. find the rate of the river current if she can travel 2 mi upstream in the same amount of time she can go 4 mi downstream.​ (let xequalsthe rate of the​ current.)

If the speed of the stream is x
Time is given by d/r , where r is the rate and d is the distance;
Rate for upstream = (15-x) mph and that of down stream is (15 +x) mph
The time taken will be the same;
Thus; 2/(15-x) = 4/(15+x)
         cross multiplying;
30 +2x = 60 -4x
   6x = 30
   x =5 
Therefore the rate of the river is 5 mph