-2+1/2 (6) I'd 1 so A is correct
Answer:
194.5315427 grams
Step-by-step explanation:
The half-life of element x would be 66 years. So, after 20 years you would have:
.5^(20/66) x 240=0.810548 x 240
=194.5315427 grams of the element left ......
The first rule you need to know is

So, you have

The second rule you need to know is

So, you have
