the 180-day prejudgment interest period was triggered by correspondence asking for reimbursement of medical treatment expenses and explaining procedures suggested by doctors). Hudspeth is also correct that the declining-principal formula should be used in calculating prejudgment interest when settlements credits are applied. Brainard, 216 S.W.3d at 816. We will not hold, however, that it was error for the trial court not to apply the declining-principal formula because — unlike her argument that her April claim triggered the 180-day period for prejudgment interest — it does not appear from the record that she ever brought this argument about declining-principal to the trial court’s attention. Tex.R.App. P. 33.1(a); Bushell v. Dean, 803 S.W.2d 711, 712 (Tex.1991) (op. on reh’g) (<HOLDING>); Inglish v. Prudential Ins. Co. of Am., 928
holding it is axiomatic that an appellate court cannot reverse a trial courts judgment absent properly assigned error holding that a ruling of the trial court to which no error has been assigned becomes the law of the case and is not subject to review by the court of appeals holding an appellate court cannot reverse a trial courts judgment absent properly assigned error holding that the court of appeals may not reverse a trial courts judgment in the absence of properly assigned error holding that it is error for court of appeals to reverse trial courts ruling that had not been objected to at the trial court level