Could anyone give a reasoning of how the Rate (R) was found in this example? How was it calculated? Could it be wrong?

- How would-our calculation change if the cash flow is received every two years? - We just need to use the appropriate discount rate - Ann receives an annuity of $450, payable once every two years - The annuity stretches out over 20 years, where the first payment occurs two years from today - The annual interest rate is 6 percent - What interest rate should we use? How many periods? PV=rC[1(1+r)T1]=0.1236450[1(1.1236)101]=2,505.57