To solve this problem, we first need to determine Dalip's speed when rowing downstream and upstream. Once we have these fundamental speeds, we can then calculate the time taken for the new specified distances.

Dalip's Upstream Time Conversion

The time provided for the upstream journey is 2 hours and 48 minutes. For accurate calculations, it's essential to convert this entire duration into hours.

• We know that there are 60 minutes in 1 hour.
• To convert 48 minutes into hours, we divide 48 by 60: $\frac{48}{60} \text{ hours} = \frac{4}{5} \text{ hours} = 0.8 \text{ hours}$.
• Therefore, Dalip's total upstream time is $2 \text{ hours} + 0.8 \text{ hours} = 2.8 \text{ hours}$.

Calculating Dalip's Speeds

We will now calculate Dalip's speed in both downstream and upstream directions using the basic formula for speed: $\text{Speed} = \frac{\text{Distance}}{\text{Time}}$.

Dalip's Downstream Speed

Dalip rows 42 km downstream in 2 hours.

• Distance downstream = 42 km
• Time downstream = 2 hours
• Downstream Speed ($\text{V}_{\text{d}}$) = $\frac{42 \text{ km}}{2 \text{ hours}} = 21 \text{ km/h}$.

Dalip's Upstream Speed

Dalip rows 42 km upstream in 2 hours and 48 minutes (which we calculated as 2.8 hours).

• Distance upstream = 42 km
• Time upstream = 2.8 hours
• Upstream Speed ($\text{V}_{\text{u}}$) = $\frac{42 \text{ km}}{2.8 \text{ hours}} = \frac{420}{28} \text{ km/h} = 15 \text{ km/h}$.

Time for New Journeys

With Dalip's downstream and upstream speeds now determined, we can calculate the time required for him to row the new specified distances: 31.5 km downstream and 22.5 km upstream.

Time for 31.5 km Downstream

Using the downstream speed ($\text{V}_{\text{d}} = 21 \text{ km/h}$):

• Distance to row downstream = 31.5 km
• Time taken downstream ($\text{T}_{\text{d}}$) = $\frac{\text{Distance}}{\text{Speed}} = \frac{31.5 \text{ km}}{21 \text{ km/h}} = 1.5 \text{ hours}$.

Time for 22.5 km Upstream

Using the upstream speed ($\text{V}_{\text{u}} = 15 \text{ km/h}$):

• Distance to row upstream = 22.5 km
• Time taken upstream ($\text{T}_{\text{u}}$) = $\frac{\text{Distance}}{\text{Speed}} = \frac{22.5 \text{ km}}{15 \text{ km/h}} = 1.5 \text{ hours}$.

Total Time Calculation

To find the total time Dalip will take for both parts of his new journey, we simply add the time taken for the downstream and upstream portions.

• Total Time = Time downstream + Time upstream
• Total Time = $1.5 \text{ hours} + 1.5 \text{ hours} = 3 \text{ hours}$.

Thus, Dalip will take 3 hours to row 31.5 km downstream and 22.5 km upstream.