Correct Answer - Option 5 : 5 hours

**Given:**

Speed of the boat against the stream = 6 kmph

**Formula used:**

Speed downstream = Speed of a boat in still water + speed of the stream

Speed upstream = Speed of a boat in still water - speed of the stream

**Calculation:**

Let downstream speed be A kmph.

⇒ 30/A + 30/6 = 8

⇒ A = 10 kmph

Speed of downstream of boat = 10 kmph

⇒ 50/10 hours = 5 hours

∴ Required time is 5 hours