A motorboat, whose speed is 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream (in km/hr) is:

• ক 2 : 3 : 4
• খ 8 : 15 : 17
• গ 3 : 4 : 5 ✅ সঠিক উত্তর
• ঘ 12 : 13 : 5