Correct Answer - Option 2 : 2 hours

**Given:**

Distance covered by boat in upstream = 10 km

Time taken by boat in upstream = 40 minutes

Distance covered by boat in downstream = 15 km

Time taken by boat in downstream = 30 minutes

Distance covered by boat in still water = 45 km

**Formula used:**

Speed of boat in still water = (Upstream speed + Downstream speed)/2

Speed = (Distance/Time)

Upstream speed = (Speed of boat) - (Speed of current)

Downstream speed = (Speed of boat) + (Speed of current)

**Calculation:**

Let the speed of boat in still water be x km/h.

and speed of current be y km/h

Time taken by boat in upstream = 40 minutes

⇒ (40/60) hour

⇒ (2/3) hour

Upstream speed = [10/(2/3)]

⇒ (x - y) = (10/2) × 3

⇒ (x - y) = 15 km/h ----(1)

Time taken by boat in downstream = 30 minutes

⇒ (30/60) hour

⇒ (1/2) hour

Downstream speed = [15/(1/2)]

⇒ (x + y) = 30 km/h ----(2)

Now, add equation (1) and equation (2)

(x - y) + (x + y) = 15 + 30

⇒ 2x = 45

⇒ x = 22.5

Speed of boat in still water = 22.5 km/h

Time taken by boat to cover a distance of 45 km in still water = [45/(22.5)]

⇒ 2 hours

∴ Time taken by boat to cover a distance of 45 km in still water will be 2 hours.