Simple interest formula is Initial Balance * (1 + tn) = Current Balance

We have

- Initial Balance = 9000
- Current Balance = 9720
- n = 2

9000 * (1 + 2t) = 9720

Divide each side by 9000

1 + 2t = 1.08

Subtract 1 from each sdie

2t = 0.08

Divide each side by 2

t =

**0.04 or 4%**