This is compounded interest.
Formula:
Future value = Present value * ( 1 + %interest / 100) ^ t
Presente value = 110
% interest = 7.25%
t = ?
Future value = 6600
=> 6600 = 1100 ( 1 + 0.0725)^t
=> 6600 / 1100 = (1.0725)^ t
=> 6 = (1.0725)^t
=> t log(1.0725) = log(6)
=> t = log (6) / log (1.0725) = 25.59
=> answer = 26 years.
