Set the equation
2p=p e^rt
2=e^rt
R interest rate 0.02
T time?
Solve for t
2=e^0.02t
Take the log for both sides
Log (2)=0.02t×log (e)
Divide both sides by log (e)
0.02t=log (2)/log (e)
Divide both sides by 0.02
T=(log(2)÷log(e))÷0.02
T=34.65 years round your answer to get 35 years
Hope it helps!