A savvy investor paid $6000 for a 20-year $10,000 mortgage bond that had a bond interest rate of 8% per year, payable quarterly. Three years after he purchased the bond, market interest rates went down, so the bond increased in value. If the investor sold the bond for $11,500 three years after he bought it, what rate of return did the investor make

(a) Per quarter, and

(b) Per year (nominal)?