80 because tens place is two over from the right
The half life of the substance is 6.92 days.
<h3>What is the Half life ?</h3>
Half life can be defined as the time required to reduce the concentration to half of its initial value.
Here the equation given is

The concentration will reduce to half therefore

so,

ln 0.5 = - 0.1001 * t(1/2)
-0.693 = -.1001 * t(1/2)
t(1/2) = 6.92 days.
Therefore the half life of the substance is 6.92 days.
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B because 2 and 1/3 is 7/3 as an improper fraction times 4 is 28/3 and as a mixed number it is 9 and 1/3