Final answer:
It would take 60 years for 32 mg of cesium-137 to decay to 8 mg, using the half-life of 30 years for cesium-137. However, this timeframe is not included in the given options, indicating an error.
Step-by-step explanation:
To find out how many years are required for 32 mg of cesium-137 to decay to 8.0 mg, we can use the concept of half-life, which is the time taken for half of the radioactive substance to decay. Cesium-137 has a half-life of approximately 30 years. If we start with 32 mg of cesium-137, after one half-life (30 years), we would have 16 mg remaining. After another half-life (another 30 years, for a total of 60 years), we would have 8 mg remaining. Therefore, it takes 60 years for 32 mg of cesium-137 to decay to 8.0 mg, which is not one of the options provided in the question, so there may be an error in the options listed.