# Help with second part of question

I'm stuck on the second question of the following problem:

The proper mean lifetime of a muon is 2.00 ms. Muons in a beam are traveling a .96c.

What is their mean lifetime as measured in the laboratory?

ans. 2.00ms/sqrt(1-.960^2)= 7.1428 ms

How far would they travel, on average, before they decay?

ans. I don't know how to do this part. Can someone help me?

Thanks.

Jessica