RBI Assistant Prelims 2016 Sitting 4 Paper

The time taken by the boat to cover a distance of (D - 56) km upstream is half of that taken by it to cover a distance of 'D' km downstream. The respective ratio between the speed of the boat downstream and that upstream is 5 : 3. If the time taken to cover (D - 32) km upstream is 4 hours, what is the speed of water current? (in km./h.)