1) linear function. The reason is that the amount of oil consumed per unit time is equal. Solution of expression: Let the driving time be X and the remaining fuel quantity be Y, and the expression of this function is Y = AX+B. Choose two sets of data in the table to get: a+b=80, 2a+b=60. Solution: a=-20, b= 100. The expression of this function is Y=-20X+ 100.

2) Expression brought into 1).

The third question is that you can't understand and answer because you can't express anything clearly.