Kenneth started saving for retirement at age 40 with plans to retire at age 70. He invested an average of $400 per month in various securities, with an average annual return of 7% adjusted for inflation. Assuming monthly compounding, how much has Kenneth saved at the start of retirement.
A. $487,988.40
B. $720,421.84
C. $37,784.31
D. $556,559.8