Explanation:

Let’s break down the problem:

- Boats P and Q go downstream from A to B.

- Time ratio (P : Q) = 4 : 5 ? Boat P is faster.

- Q’s speed in still water = 34 km/h; Stream speed = 6 km/h

- Q’s downstream speed = 34 + 6 = 40 km/h

- Since time ? 1/speed for same distance,

*(Speed of P) : 40 = 5 : 4 ? Speed of P downstream = 50 km/h*

- To find P’s speed from B to A (upstream):

Upstream speed = Boat’s speed in still water - stream speed

Let boat speed in still water = x

So, x + 6 = 50 ? x = 44 km/h

- P’s upstream speed = 44 - 6 = 38 km/h

- Correct option is: Option:4, 38 km/h