Step 1: Calculate Time for the First Part

The first part of the journey covers a distance ($d_1$) of 30 km at a speed ($s_1$) of 6 km/hr.

The time taken ($t_1$) is calculated using the formula: Time = Distance / Speed.

$t_1 = \frac{d_1}{s_1} = \frac{30 \text{ km}}{6 \text{ km/hr}} = 5 \text{ hr}$

Step 2: Identify Details for the Second Part

The second part of the journey has a distance ($d_2$) of 40 km and the time taken ($t_2$) is given as 5 hr.

Step 3: Calculate Total Distance and Total Time

Total distance ($D$) is the sum of distances of both parts:

$D = d_1 + d_2 = 30 \text{ km} + 40 \text{ km} = 70 \text{ km}$

Total time ($T$) is the sum of times taken for both parts:

$T = t_1 + t_2 = 5 \text{ hr} + 5 \text{ hr} = 10 \text{ hr}$

Step 4: Calculate Average Speed

Average speed ($S_{avg}$) is calculated by dividing the total distance by the total time:

$S_{avg} = \frac{\text{Total Distance}}{\text{Total Time}} = \frac{D}{T}$

$S_{avg} = \frac{70 \text{ km}}{10 \text{ hr}} = 7 \text{ km/hr}$

Conclusion: Average Speed Result

The average speed for the whole journey is 7 km/hr.