Upgraded to new computer and now Numbers will not open excel files

I was running Numbers on a 10.6 machine just fine. I upgraded to a new machine with Yosemite and Number pre-installed and now it will not open any excel files. These are the same files I was opening with Numbers on my older machine. I did back up my old drive on time machine and restored files only onto the new machine. I am just looking here for a possible solution. I moved Numbers to the trash and tried to go to the App Store to reinstall but it was listed for 19.99 to purchase. Any ideas? Thanks!