When the relationship between two variables are said to be proportional, it means that one variable is a constant multiple of the other variable. They are related by a constant of proportionality, usually denoted as k.
In this problem, the dependent variable is the distance in kilometers. Your mileage is limited with the amount of fuel you have. Thus, the independent variable is the liters of fuel. When these two are proportional, it could be expressed as
distance = k * liters of fuel, such that
distance/liters of fuel = k
By variation,
distance,1/liters of fuel,1 = distance,2/liters of fuel,2, where 1 denotes situation 1 and 2 denotes situation 2. Therefore,
999999 km /999 liters = x km /121212 liters, where x is the unknown distance. We can now therefore find the value of x.
x = (999999*121212)/999
x = 121333212 kilometers
