Question 1170820
Rule of 70 (70/4.6=15.22) suggests C
3500=1750(1.046)^n
2=1.046^n
ln2=n ln 1.046 
0.693/0.0445=n.  The 0.693 is the decimal of 69.3%, and that is why the Rule of 70 exists for doubling. Some use 72, since so many more numbers divide evenly into it.
n=15.41 years.
C