Question 1139827
The first is 2800(1+(0.12/6))^6n=5600
or 2=1.02^6n
ln2=6n*ln(1.02)
6n=35.002
n=5.834 years

rule of 72 would say 6 years so reasonable result.

continuously is 2=e^rt, where P=Poe^rt, and P=2Po
so ln2=rt
ln2/0.12=t
t=5.776 years.