Keith started saving for retirement at age 45 with plans to retire at age 70. He invested an average of $500 per month in various securities, with an average annual return of 6% adjusted for inflation. Assuming monthly compounding, how much has Keith saved at the start of retirement? (show work)
A= $27,432.26
B= $446,496.98
C= $346,496.98
D= $712,355.15