Then the borrower shall from time to time pay to the lender upom demand such amounts as the lender certifies as necessary to compensate it for such invreased cost or reduction on and from the date that increases cost or reduction is incurred or suffered and, subject tp payment thereof, the borrower may prepay the Loan in full together with all interest accrued thereon and all other sums due and payable under this agreement on the then interest paent date, without repayment fee, rovided that the lender shll have received not less than 30 days' prior written notice of such prepayment