Option 2 : 15 km

**Given:**

The speed of the boat = 8 km/h

The speed of the stream = 2 km/h

Time taken by the boat to go to a place and comeback = 4 hours

**Formula Used:**

Upstream speed = (Speed of the boat) - (Speed of the stream)

Downstream speed = (Speed of the boat) + (Speed of the stream)

Distance = Speed × Time

**Calculation:**

Upstream speed = (8 - 2) km/h

⇒ 6 km/h

Downstream speed = (8 + 2) km/h

⇒ 10 km/h

Let the distance of the place be x km.

According to the question,

(x/6) + (x/10) = 4

⇒ [(5x + 3x)/30] = 4

⇒ 8x/30 = 4

⇒ x = 15

**∴ The distance of the place will be 15 km.**

__Additional Information__

1) Upstream**:** The boat or a swimmer moving against the stream is known as moving upstream (against the flow of water).

2) Downstream**:** The boat or a swimmer moving along the stream is known as moving downstream (along the flow of water).

3) If the speed of the boat or swimmer is X km/hr and the speed of the stream is Y km/hr,

a) The speed of the boat or swimmer in the direction of the stream is known as speed downstream. It is given by;

Speed downstream = (X + Y) km/hr

b) And, the speed of the boat or swimmer against the stream is known as speed upstream. It is given by;

Speed upstream = (X - Y) km/hr