A utility bills electricity in tiers. Write electricity_bill(kwh) that returns the amount due as a float rounded to 2 decimals:
- the first 100 kWh cost 0.10 each
- the next 200 kWh (from 100 up to 300) cost 0.15 each
- every kWh above 300 costs 0.25
- a fixed service charge of 5.00 is added whenever any electricity was used at all; a customer who used nothing pays 0.0
Examples
Input: kwh = 0
Output: 0.0
Input: kwh = 100
Output: 15.0
Explanation: 100 * 0.10 = 10.0, plus the 5.00 service charge.
Input: kwh = 350
Output: 57.5
Explanation: 5 + 10 (first 100) + 30 (next 200) + 12.5 (50 at 0.25).
Constraints
0 <= kwh <= 10**6
Goals
- Charge each block of usage at its own rate
- Add a fixed charge only when there is any usage
- Round money to two decimals