Speed of a boat in still water is 15 km/h while the speed of stream is ____ km/h. Total time taken by the boat to go 150 km upstream and 225 km downstream is ____ hours. The values given in which of the following options will fill the blanks in the same order in which it is given to make the above statement true:
I. 5, 45
II. 8, 40
III. 10, 37.5
IV. 6, 35

For I: Speed of boat = 15 km/h Speed of stream = 5 km/h Speed in upstream = 15 – 5 = 10 km/h Speed in downstream = 15 + 5 = 20 km/h Total time = 150/10 + 225/20 = 15 + 11.25 = 26.25 hours So, I can’t be the answer. For II: Speed of boat = 15 km/h Speed of stream = 8 km/h Speed in upstream = 15 – 8 = 7 km/h Speed in downstream = 15 + 8 = 23 km/h Total time = 150/7 + 225/23 = ~21.43 + ~9.78 = ~31.21 hours So, II can’t be the answer. For III: Speed of boat = 15 km/h Speed of stream = 10 km/h Speed in upstream = 15 – 10 = 5 km/h Speed in downstream = 15 + 10 = 25 km/h Total time = 150/5 + 225/25 = 30 + 9 = 39 hours So, III can’t be the answer. For IV: Speed of boat = 15 km/h Speed of stream = 6 km/h Speed in upstream = 15 – 6 = 9 km/h Speed in downstream = 15 + 6 = 21 km/h Total time = 150/9 + 225/21 = 16.67 + 10.71 = 27.38 hours So, IV can’t be the answer.