On google, it says 8.463.
Answer:

Step-by-step explanation:
The time constant of the isotope is:


The decay of the isotope is described by the following model:

Now, the time is cleared in the equation:



Answer:
D
DDDDDDDDDDDDDDDDDDDDDDDDDDDD
Step-by-step explanation:
Slope is change in y over change in x.
Change in y is -9
Change in x is +12
So -9/12 or -2/3
Answer -2/3