Since the amount of oil in the tank decreases constantly, we need to create a linear function. Using the base form, y = mx + b, we can replace -6 for m because volume decreases by 6 (or increases by -6) each hour, and +70 for b because we start off with 70 liters of oil. So we get y = -6x + 70, with x representing the number of hours, and y representing the volume of oil remaining.
