Explanation:

Let’s break down the problem:

- Total Payment = Rs. 6 per km × Distance + Cost of Diesel (Rs. 40/litre × litres used)

- For each car, let the distance travelled be D.

- Diesel used = D ÷ Mileage.

- Payment equation: Total = 6D + 40 × (D / Mileage)

- Rearranged: Total = D*[6 + (40 / Mileage)]  ?  D = Total / [6 + (40 / Mileage)]

- Speed = Distance / Hours

Calculate for each car:

Car A:

- Cost per km: 6 + (40/8) = 11

- D = 2120 / 11 = 192.73 km

- Speed = 192.73/20 = 9.64 kmph

Car B:

- Cost per km: 6 + (40/10) = 10

- D = 1950/10 = 195 km

- Speed = 195/25 = 7.8 kmph

Car C:

- Cost per km: 6 + (40/9) ˜ 10.44

- D = 2064/10.44 ˜ 197.7 km

- Speed ˜ 197.7/24 ˜ 8.24 kmph

Car D:

- Cost per km: 6 + (40/11) ˜ 9.64

- D = 1812/9.64 ˜ 188 km

- Speed ˜ 188/22 ˜ 8.55 kmph

Car A has the highest average speed of 9.64 kmph.

Option:1, Car A is correct.