Question 1069102
A=Aoe^rt is continuous compounding.  The problem doesn't say.
A=2Ao
A/Ao=2
2=e^rt, and t is known to be 5
2=e^5r
ln both sides
ln 2=5r
r=ln2/5=13.86%
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at 8 times  we then have 
8=e^(13.86t)
ln of both sides
ln 8=.1386 t
t=ln 8/.1386=15.00 years
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(1+.06/2)^2=1.0609
subtract 1
0.0609 or 6.09%