The first step to having a good solution in the present question, building an equation that gives us the number of Gallons (G) in the function of rate miles/gallons in the city (C) and miles/gallons in the highway (H).
We know that in typical weeks Jon drives 20miles in the city (Dc) and 60 miles on highway (Dh) (Going + Coming Back from his parent's house).
The rates of the number of gallons per mile are calculated as follows:
Anthe total number of gallons is equal to the sum of each case:
Now, to solve the problem, we just need to substitute the values as follows:
A - I)
The present car has the given rates:
Substituting:
A-II)
The new values are:
Substituting, we have:
A-III
The difference for 52-week year is equal to the difference for a single week times 52, as it is calculated as follows: