Answer:
The differential equation is 
Step-by-step explanation:
Differential equation for the rate of change in radiation level:
Radiation level is R.
Rate of change indicates that the radiation level R varies in function of time t, which mathematically means that we have:

After the reactor is shut down, the radiation from the nitrogen-17 decreases in such a way that the rate of change in the radiation level is directly proportional to the radiation level.
Rate of change is k. Decreases means that k is negative. Proportional to the radiation level of R means that -k multiplies R. So the differential equation is:

Answer:
See below
Step-by-step explanation:

Hence, both ratios are equal to each other
It should be the 2nd or 4th answer, i’m not COMPLETELY sure. I’m positive it’s the 4th answer
Answer:
The circumference is 81.64cm
Step-by-step explanation:
Circumference of a circle=2×3.14×radius
2×3.14×13=81.64
I hope this helps you in any way :)