Stuck on a problem in this physics assignment. Unsure whether or not I should use the ?t' = t / sqrt (1- v^2/c^2).

Problem~

An elementary particle called a pi meson (or pion for short) has an average lifetime of 2.6 10-8 s when at rest. Suppose that a pion moves with a speed of 0.9c relative to Earth.

(a) Find the average lifetime of the pion as measured by an observer on Earth.

s

(b) Find the average distance traveled by the pion as measured by the same observer.
m

(c) How far would the pion have traveled relative to Earth if relativistic time dilation did not occur?
m

View the original article here