(1) The sum payable is a sum certain even though it is to be paid

1. (a) with stated interest or by stated installments; or
2. (b) with stated different rates of interest before and after default or a specified date; or
3. (c) with a stated discount or addition if paid before or after the date fixed for payment; or
4. (d) with exchange or less exchange, whether at a fixed rate or at the current rate; or
5. (e) with costs of collection or an attorney's fee or both upon default.