If the interest rate on U.S. treasury bonds that mature in one year is 2.2%, the interest rate on U.S. treasury bonds that mature in two years is 3.9%, the interest rate on U.S. treasury bonds that mature in three years is 5.1%, and the interest rate on U.S. treasury bonds that mature in four years is 5.9%, what is the one year forward rate for year 2 (i.e., f₂ )?