ANSWER
The amount of sample left after 120 years is 21.9 grams
Step-by-step explanation
Given that;
The original mass of the sample is 700g
The half life of the sample is 24 years
Time is 120 years
Follow the steps below
Step 1; Write the half-life formula
Step 2; Substitute the given data into the above formula
Therefore, the amount of sample left after 120 years is 21.9 grams