Use the DerivaGem software to value $1 \times 4,2 \times 3,3 \times 2$, and $4 \times 1$ European swap options to receive floating and pay fixed. Assume that the 1-, 2-, 3-, 4-, and 5-year interest rates are $3 \%, 3.5 \%, 3.8 \%, 4.0 \%$, and $4.1 \%$, respectively. The payment frequency on the swap is semiannual and the fixed rate is $4 \%$ per annum with semiannual compounding. Use the lognormal model with $a=5 \%, \sigma=15 \%$, and 50 time steps. Calculate the volatility implied by Black's model for each option.