Working Out My Desired Income in Haskell

1. desiredIncome x = x > $3000 per month after tax and superannuation contributions
2. Tax = $4650 + 30% of per-annum income between $37,000 and $80,000

Eventually I'd like something that takes all of my expenses into account and calculates the desired income as well, so it's for general use not just personal.  For now, this is a good start.