680 - Math - Problem Solving

Question: A sum of money invested for a certain number of years at 8% p.a. simple interest grows to Rs.180. The same sum of money invested for the same number of years at 4% p.a. simple interest grows to Rs.120 only. For how many years was the sum invested?

1. 25 years
2. 40 years
3. 33 years and 4 months
4. Cannot be determined