Mural, a wallpaper hanger, sent Gennybelle, a general contractor, this telegram: Will do all paperhanging on new Doctors' Building, per owner's specs, for $14,000 if you accept within reasonable time after main contract awarded./s/ Mural Three other competing hangers sent Gennybelle similar bids in the respective amounts of $18,000, $19,000, and $20,000. Gennybelle used Mural's $14,000 figure in preparing and submitting her own sealed bid on Doctors' Building. Before the bids were opened, Mural truthfully advised Gennybelle that the former's telegraphic sub-bid had been based on a $4,000 computational error and was therefore revoked. Shortly thereafter, Gennybelle was awarded the Doctors' Building construction contract and subsequently contracted with another paperhanger for a price of $18,000. Gennybelle now sues Mural to recover $4,000. Which of the following, if proved, would best support Mural's defense? 
Gennybelle gave Mural no consideration for an irrevocable sub-bid. Mural's sub-bid expressly requested Gennybelle's acceptance after awarding of the main contract. Even after paying $18,000 for the paperhanging, Gennybelle would make a net profit of $100,000 on the Doctors' Building contract.  Before submitting her own bid, Gennybelle had reason to suspect that Mural had made a computational mistake in figuring his sub-bid. 