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Verified answer

(х-3/xy-x^2) -(3-y/xy-y^2)=(x-3/x(y-x))- (3-y/y(x-y))=xy-3y+3x-x/xy(y-x)=3x-3y/xy(y-x)=-3(x-y)/ xy(x-y)=-3/xy