The half-life of carbon-14 is 5730 years. how long will it take for 7/8 of a sample of carbon-14 to decay

The half life of Carbon-14 is 5730 years, how many years would it take for 7/8 of the original amount to decay? 

Can somebody please help with this problem. I *think* I understand the basics of what a half life is. If I learned correctly, its the amount it takes for half of a sample to decay. It should also happen exponentially, 1/2 remaining after one half life, 1/4 after the second, 1/16 after the third etc. I'm still a little shaky though. Could somebody please clarify what exactly a half life is and how it can be determined (i.e. how to find the time it would take for 7/8 to decay)