John has to pay taxes.  He earned $100,000 for the year.  He has $30,000 in deductions.  The first $20,000 of taxable income is taxed at 10%.  The rest is taxed at 20%.  How much does he pay in taxes?
His taxable income is 100,000-30,000=$<T>subtract(100000, 30000)=70000
So he pays 20,000*.1=$<T>multiply(20000, 0.1)=2000.0 tax at the lower rate
He has to pay 70,000-20,000=$<T>subtract(70000, 20000)=50000 at the higher rate
The taxes for that is 50,000*.2=$<T>multiply(50000, 0.2)=10000.0
So his total tax bill is 10,000+2,000=$<T>add(10000, 2000)=12000
