LETTER AGREEMENT

Exhibit (d) 3.18

LETTER AGREEMENT

State Street Bank and Trust Company

P.O. Box 1713

Boston, MA 02105

Re: Yield Calculation Services Agreement

Pursuant to Section 10 of the Amended and Restated Yield Calculation Services Agreement of Xxxxxxx Investment Company (“RIC”), dated August 1, 2006, XXX advises you that it is creating six new funds to be named the 2015 Strategy Fund, 2025 Strategy Fund, 2035 Strategy Fund, 2045 Strategy Fun, 2050 Strategy Fund and In Retirement Fund (the “New Funds”). RIC desires for State Street Bank and Trust Company to compute the performance results of each class of each New Fund pursuant to the terms and conditions of the Amended and Restated Yield Calculation Service Agreement. The fees to be charged by you in return for your services are set forth in the Amended and Restated Yield Calculation Services Agreement.

Please indicate your acceptance to amend the Amended and Restated Yield Calculation Service Agreement by executing this letter agreement and returning it to the undersigned.

Sincerely,

XXXXXXX INVESTMENT COMPANY

By:

Xxxx X. Xxxxxxx

Treasurer

Accepted this          day of                     , 2008

STATE STREET BANK AND TRUST COMPANY

By:

Its: