A medical laboratory stock solution is prepared by an initial activity due to 24 Na of 3.0 mCi/mL, and 20.0mL of the stock solution is diluted at t0 = 0to a working solution whose total volume is 250 ml. After 48 h, a10.0 mL sample of the working solution is monitored with a counter. What is the measured activity? (Note that 1 mL = 1 millilitre.)