Detailed 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.
Q: Problem: a person crosses a 1080 m long street in 12 minutes. what is his speed in km per hour ?
Options: a. 4.1, b. 4.5, c. 4.8, d. 5.4, e. 5.5
A:
d