"In Virginia property settlement and separation agreements are contracts and subject to the same rules of formation, validity and interpretation as other contracts." Smith v. Smith, 3 Va. App. 510, 513, 351 S.E.2d 593, 595 (1986). "The essential elements of a cause of action for breach of contract are: (1) 'a legal obligation of a defendant to the plaintiff; (2) 'a violation or breach of that right or duty,' and; (3) 'a consequential injury or damage to the plaintiff.'" Westminster Investing Corp. v. Lamps Unlimited, 237 Va. 543, 546, 379 S.E.2d 316, 317 (1989) (quoting Caudill v. Wise Rambler, 210 Va. 11, 13, 168 S.E.2d 257, 259 (1969)). "While it is true upon the breach of a valid and binding contract the law infers nominal damages, it does not infer or presume substantial or compensatory damages. The latter must be proven by competent evidence." Orebaugh v. Antonious, 190 Va. 829, 834, 58 S.E.2d 873, 875 (1950). The party alleging a breach has an "obligation to establish his damages with reasonable certainty by the best evidence which is available." White Sewing Mach. Co. v. Gilmore Furniture Co., 128 Va. 630, 650, 105 S.E. 134, 140 (1920). "Proof with mathematical precision is not required, but there must be at least sufficient evidence to permit an intelligent and probable estimate of the amount of damage." Hailes v. Gonzales, 207 Va. 612, 614, 151 S.E.2d 388, 390 (1966). In adjudicating a contractual dispute, evidence provided by an expert is "admissible . . . if it will assist the fact finder in understanding the evidence," Tittsworth v. Robinson, 252 Va. 151, 154, 475 S.E.2d 261, 263 (1996), but it must "be based on an adequate foundation." Keesee v. Donigan, 259 Va. 157, 161, 524 S.E.2d 645, 647 (2000). "Expert testimony is not relevant and probative if it is founded on assumptions that have an insufficient factual basis." 259 Va. 157, 161, 524 S.E.2d 645, 648.