Inflation and Unemployment

Question:

Masako buys a house in 1999. She obtains a mortgage that carries an annual interest rate of 12 per cent, and makes payments of $880 per month. The CPI in 1999 is 100, in 2000 it is 110, and in 2001 it is 120. What is the real interest rate in 2001?

4 per cent

3 per cent

21 per cent

9 per cent