[Sale of KyRo's Toys] Ky and Roland Owned KyRo's Toy

[Sale of KyRo's Toys] Ky and Roland owned KyRo's Toy Distributors together for many years. After years of arguing about sharing an office, they decided they no longer wanted to work together, even though each wanted to remain in the toy distribution business. They asked their accountant, Delia, to separate the accounts equitably, and she prepared a spreadsheet showing the value of KyRo's accounts, and an equitable division of those accounts. Ky and Roland reviewed the division of accounts and signed a separation agreement that included a phrase that the accounts would be divided 50-50 as per Delia's spreadsheet attached to the agreement. Both Ky and Roland signed a disclaimer that stated that they had reviewed the attachment. Six months later, when commissions arrived for the two separate companies, Ky noticed that he was making substantially less than one-half of what he made with KyRo, and upon investigation, realized that some of the financial information on which Delia had relied in preparing the spreadsheet had been outdated, and the accounts, were in fact, not divided equally. Ky now wants to rescind the separation agreement, claiming that all three elements of mutual mistake are present, and that the mistake about the division of accounts had a material effect on the agreement because it was not what was intended.
-What must Ky show in order to meet the third requirement necessary to prove mutual mistake?

A) That enforcement of the contract would have an adverse effect on the party who did not agree to bear the risk of mistake.
B) That enforcement of the contract would not have an adverse effect on either party.
C) That enforcement of the contract would have an adverse effect on both parties.
D) That failure to enforce the contract would have an adverse effect on both parties.
E) That failure to enforce the contract would have an adverse effect on only one party.