the half-life of uranium-232 is 69 years. If the nuclear byproduct contains uranium-232, it is not considered safe for human contact until 99.2% of it has been decayed. How long will this take

After 69 years, 50% of the element has decayed
After 1 year, then,
x = 0.5/69 = 0.00724
0.724% of uranium-239 has been decayed.
To find how long it will take for 99.2% of the element to decay, we can use a similar method:
x years/0.992 = 69 years/0.5
x = 136.896 years
Therefore, it will take 136.896 years for 99.2% of the nuclear byproduct to have decayed.
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The answer is b because a,c,and d are opinons