Numbers App (v3.5.3) Freezes on MacBook Air

I just started having problems today with the Numbers App (version 3.5.5 2150) on my MacBook Air (5.1, 4Gb memory, OSX Yosemite 10.10.3). I open it, select a template or existing document, and within a minute or so it lockups - 'Spinning Wheel of Death'. Maybe I have Mail or Google or Safari running in the background, but nothing else. I have rebooted, deleted the app and rebooted then reloaded it - twice. Nothing seems to be helping. Does not matter which file I am in or if its a new file, give it a minute and it locks up. Sometimes I'm inserting data, other times I'm not touching the keyboard and it locks up, all within a couple of minutes of starting the app. Activity monitor states that Numbers is not responding. Any ideas? Currently accessing the my files using my iPad which is OK for a quick update of data, but not for long periods of time. Thanks!!!