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i think because we need to input (-) before enter the PV.
becomes PV= 65,559.73, n=3, i=10% -> PMT = -26,362.54
Because the question asking about "OPTIMAL’, choose the lowest PMT (read : Cost).
Of course this is different question with practice exam Schweser afternoon session no 88 (Volume 1) or CFAI Web Question (Scott) no 6 where we choose the project based on highest PMT.
juts my opinion as candidate.