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Question: 

A $\textbf{light-year}$ is the distance light travels in one year (at speed $= 2.998 \times 10^8 \textrm{ m/s}$).
(a) How many meters are there in $1.00 \textrm{ light-year}$?
(b) An astronomical unit $\textrm{(AU)}$ is the average distance from the Sun to Earth, $1.50 \times 10^8 \textrm{ km}$. How many $\textrm{AU}$ are there in $1.00 \textrm{ light-year}$?

Giancoli, Douglas C., Physics: Principles with Applications, 7th Ed., ©2014. Reprinted by permission of Pearson Education Inc., New York.

Quick Answer: 

a) $9.46 \times 10^{15} \textrm{ m}$
b) $6.31 \times 10^4 \textrm{ AU}$

Giancoli 7th Edition, Chapter 1, Problem 19

(1:50)