Answer: You need to find the radius...
Step-by-step explanation:
A(t) = Ao*e^(-rt)
-rt = ln [ A(t)/ Ao]
t = - ln [ A(t)/ Ao] / r
r= 0.0124% = 0.0124/100 = 0.000124
A(t)/A0 = 10% = 10/100 = 0.1
Now substitute
t = - ln [0.1] / 0.000124 = 2.3025851 / 0.000124 = 18,569 years
Your result will depend on how you round ln(0.1).
8, because the two minuses add up and turn into positive and 1/5 adds to 4/5 and turns into a whole 1 and adds 7 equal 8
