9.5 years. The reason being you need to use the formula P(t)= P e kt in which you would get 2= 0.073t
Then you would write the equation as ln(2)= 0.073t
After you put the number on the same side and get t= ln(2)/ 0.073
And then you get and answer of 9.49 year which would round up to 9.5
