Instructions: 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.
Input: Problem: a start walking from a place at a uniform speed of 4 kmph in a particular direction. after half an hour, b starts from the same place and walks in the same direction as a at a uniform speed and overtakes a after 1 hour 48 minutes. find the speed of b.
Options: a. 4.7 kmph, b. 4.6 kmph, c. 4 kmph, d. 7 kmph, e. 5.3 kmph
Output:
b