Given a math problem with context and a question and 5 answer choices, the task is to provide the correct answer choice based on the problem. You must choose one of the given answer choices by letter: a, b, c, d, or e; anything else is invalid.

Problem: in traveling from a dormitory to a certain city, a student went 1 / 3 of the way by foot, 3 / 5 of the way by bus, and the remaining 2 kilometers by car. what is the distance, in kilometers, from the dormitory to the city ?
Options: a. 30, b. 45, c. 60, d. 90, e. 120
a

Problem: the speed of the boat in still water in 12 kmph. it can travel downstream through 48 kms in 3 hrs. in what time would it cover the same distance upstream ?
Options: a. 8 hours, b. 6 hours, c. 4 hours, d. 5 hours, e. 6 hours
e

Problem: yesterday it took robert 3 hours to drive from city a to city b. today it took robert 2.5 hours to drive back from city в to city a along the same route. if he had saved 30 minutes in both trips, the speed for the round trip would be 80 miles per hour. what is the distance between city a and city b ?
Options: a. 90, b. 180, c. 150, d. 240, e. 300

b