The question has missing details. However, general questions that could be asked is as follows:
(1) The number of miles traveled after using (say) 5 gallons
(2) The number of gallons used after traveling for (say) 36 miles
Answer:
See Explanation
Explanation:
Given

A linear equation is represented as:

Where
and

c, in this question represents the initial capacity of the tank.
So, the initial capacity is 120 liters
Solving (a): r = 5




60 miles traveled
Solving (b): s = 36


Collect like terms


Solve for r

42 gallons used