Answer:
The lorry travels by 6 mph more than the expected speed.
Explanation:
Velocity formula:
Velocity is distance divided by time, that is:

Shortest route:
400 miles in 10 hours, which means that
. So

In mph.
The lorry actually travels by a different route which increases the distance by 15%, but it still arrives in 10 hours.
Distance is multiplied by 100% + 15% = 115% = 1.15, so:

Then

46 mph
By how many more mph than the expected speed does the lorry travel?
46 - 40 = 6 mph
The lorry travels by 6 mph more than the expected speed.