Numbers 2,4,6,8 please show work

1. A Phosphorous-32 source has a half-life of 14.28 days and had an activity of 75,000 dpm as of 12/2/92. What was the activity as of 12/28/92 ? 2. A 55nCi90Sr source was assayed on 6/1/88. What would the activity be on 6/1/93 ? (The half-life of 90Sr is 29.1 years) 3. An 60mCi iodine solution of 131I was created and then left on a laboratory shelf for two weeks before it was used. What was the activity of the solution at the time it was used? (Iodine- 131 has a half-life of 8.04 days) 4. A radon air sample was collected and then counted 4 hours later. If the sample count showed an activity of 5E4pCi, what was the activity on the sample at the time it was collected? (Radon-222 has a half-life of 3.8235 days) 5. A 10.5Ci60 Co radiography source was prepared 3 years ago, having a half-life of 5.271 years. What is the activity today? 6. A pure alpha source reads 244,000 dpm today. It is a 210 Po source which has a half-life of 138.38 days. If the source was manufactured a year ago, what the activity at the time it was manufactured? 7. A137Cs source has an activity of 750mCi, with a half-life of 30.17 years. How long will it take for the source to be read less than 100mCi ? 8. An air sample was collected in a thorium storage building and was counted immediately, yielding 2.5E3pCi/. The sample was recounted 5 minutes later giving an activity of only 59.4pCi/L. What is the half-life and the most likely isotope on the sample