Apollo 13 was meant to land in the Fra Mauro area of the moon. Unfortunately an explosion on board Apollo 13 forced it to circle the moon without landing. So, the Fra Mauro site was reassigned as the landing site for Apollo 14. Apollo 13 was the third lunar landing attempt and even though it didn’t land on the moon it was considered a “successful failure,” because of the experience gained in rescuing the crew.
After everything went wrong, they needed to get home fast and they had to stretch their 45 hour lifespan of the aircraft to 90 hours. Oxygen wasn’t really a concern, but power and water were major concerns in the descent process of returning back to Earth. Removing the carbon dioxide from the capsule was also a concern. Upon entering the Earth’s atmosphere it was raining and water actually got inside of the command module from where the oxygen had escaped.