i need an excel expert

I am making a tax software for my company I want to make medicare levy calculator. So what i am doing like suppose the income bracket is 42000-43,999 and medicare levy for one children is $210.30 for the income of 42000. Now as income increase by $1 the medicare levy increase by $.10 so to write numbers till 43,999 is very difficult. So i need some formulae so I put any number between 42000-43999 and it automatically comes with a correct medicare levy. Example the income lets suppose 42003 so income is increased by dollar 3 and the medicare levy is increased by $.30. so now total medicare levy is $210.30+$0.30 = $210.60. I need a formula to calculate on income $42560 so what will be the medicare levy.