An investor buys a 5 year $450,000 treasury notes with an interest rate of 10%. The investor expects to earn $45,000 per year from such investment. However, at the end of the term, interest rates are 5%. If the investor buys another 5 year $450,000 treasury notes they will only earn $22,500 rather than $45,000 which was earned initially.

I need help understanding the reinvestment risk in this scenario. Is there a calculation? Can someone explain please