Thank you for your reply. I've been studying what you've posted for a bit, and have tried applying it.

k=.693/22 years = .0315 for the decay constant, and use your first equation to multiply .0315 by 2.65x10^{21} to get 8.3x10^{19}.

According to the textbook, the answer for this should be 2.6x10^{12}. The activity in curies is supposed to be 71 curies.

I've tried this problem for a while now, and still can't come up with the answers from the textbook