Week 1: 10 hours worked - 1 hour banked = 9 hours paid @ $10 / hour = $90.

Week 2: 10 hours worked + 1 hour withdrawn = 11 hours paid @ $20 / hour = $220.

Week 1 + Week 2 = $310.


It's precisely because you're banking hours (not money) that the hour you bank today ("low pay") is worth more when you withdraw it tomorrow ("higher pay"). The same total number of hours worked will result in more money earned (ignoring all issues of TVM, human nature of actually working fewer hours, etc.).