$[2/3$ Points$]$

The half$-$life of cesium$-137$ is $30$ years. Suppose we have a $120$ mg sample.

$($a$)$ Find the mass $($in mg $)$ that remains after $t$ years.

$y(t)=$

mg

$($b$)$ How much of the sample $($in mg $)$ remains after $70$ years? $($Round your answer to two decimal places.$)$

$$ mg

$($c$)$ After how many years will only $1$ mg remain? $($Round your answer to one decimal place.$)$

$t=$ yr

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