Deleting rows in a large data sample

Hi all,

What methods do you suggest for deleting rows in the data sample below? I need to get rid of firms with "n.a." values or zeros more than 7 per variable, meaning that I need at least 3 observations per variable. So, for instance if the investments variable has only 2 observations over the 10 years of data that specific firm (row) should be deleted.

Thanks in advance for your help, I couldn't find any good solutions for this specific problem with the help of mr. google

Ps. I'm running Office 2011 for Mac

I found a work around for the problem already, but your way looks easier. Thanks a lot!