Answer:

Step-by-step explanation:
Given,
The number of litres consumed by car in (x+20) km = 6,
So, number of litres consumed by car in 1 km =
,
Now, number of litres consumed by car in 100 km = 100 × litres consumed by car in 1 km


Hence, the rate of fuel used by his car would be
litres per 100 km.