(2) When a=320:

Residual oil in the oil tank = 20-0.06x320 = 0.8 > 0.

∴ There is enough oil in the fuel tank;

(3) According to the meaning of the question:

20-0.06a≥0

∴0.06a≤20

∴a≤ 1000/3

A is an integer.

The maximum integer value of ∴a is 333.

Then, the maximum integer value that can guarantee the driving distance of the car is 333 kilometers.

I am glad to solve the above problems for you, and I hope it will help your study! ≤、≥ ∠