So you want to find out the distance for both the cities. Since there are 8 inches to both cities, then the answer would be 160 miles since every inch would equal to 20 miles, which is the actual distance.
I'm sorry that I'm not in calculus, but hopefully I can help. Personally, I would choose: D.) x; in the second equation ; because it has easier numbers to figure out, you'll get it eventually...