I have purchased I bond from TreasuryDirect in the amount of $10K in 8/2021 and 1/2022, totaling $20K. Currently, TreasuryDirect shows the interest rate of 9.62% for my 8/2021 purchase and 6.48% for my 1/2022 purchase. The current value of my I bonds are $21,312.00. How did TreasuryDirect calculate this current value? Thank you.