A 1.00-g sample of carbon from a modern source gave 15.3 disintegrations per minute. A sample of carbon from an "old" source gave 920 disintegrations per hour. What is the age of the "old" sample of carbon? The half-life of carbon-14 is 5.73103 year.

1. about 345,000 years

2. about 20 million years

3. about 34,400 years

4. less than a few years