[Simplicity]

This was a problem given in a problem set....but I'm kinda confused as to how to start....in addition to some notation. I attached it because I can't figure out how to get Latex or hide tags going (first time on this forum)

[Borek]

You will need initial sample activity. Was it given to you? Perhaps it is listed in the book? In general it is not a constant value, but for a simple question you probably don't have to look for the calibration data.