Radioactive element ‘A’ decays over time to element ‘B’. Element ‘A’ has a half-life span of 5 days. If you started with 20 grams of A and 0 grams of B, how many grams of B would there be after a total of 10 days?

1) 0 grams

2) 2.5 grams

3) 5 grams

4) 7.5 grams

5) 10 grams

6) 12.5 grams

7) 15 grams

8) 17.5 grams

9) 20 grams

10) 22.5 grams

11) 25 grams

12) 27.5 grams