Answer:
The answer to your question is 120 years
Explanation:
Data
half-life = 30 years
decay of 1/16
Process
1. Do a chart to solve this problem
Every 30 years the amount of Cesium is half the previous amount.
Amount of Cesium-137 Time (years)
x 0
x/2 30
x/2/2 = x/4 30
x/4/2 = x/8 30
x/8/2 = x/16 30
Total time = 30 + 30 + 30 + 30 or 4 x 30 = 120 years