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:



I think its (B)
V = four-thirds pi r cubed = Four-thirds (3.14) (5) cubed
You first need to make the denominators on both fractions the same and how to do that is simple. What does 6 and 8 go into to? Well, the answer is 24. You multiply 5/6 into 4 and you should get 20/24. Then, you multiply 3/8 into 3 and you should get 9/24. Now the last part is easy, you just subtract 20/24 and 9/24 and you should get 11/24 as your answer. It cannot be simplified. Hope it helped.
615.44 rounded to the nearest tenth is 615.4