Elsinore Union Elementary School District (P) invited contractors to prepare bids for additions to the district's school buildings. Kastorff (D), a building contractor, prepared worksheets using bids from various subcontractors. The first sub-bid D received for plumbing was for $9,285. D thought that he wrote it down on the sheet, but he did not. When D got a lower bid of $6,500 for the plumbing work, he subtracted $3,000 from the total amount of his bid. D's total bid of $89,994 included no allowance for the plumbing work. D's bid was the lowest by $11,306. The school board inquired if the bid was correct. D affirmed that his bid was correct after he asked his clerical assistant, who assured him that it was. D was awarded the contract. D discovered the error the very next day. D rescinded the bid. P then awarded the contract to P. P returned it and again explained his error and asked for reconsideration. P refused to release D. The school board then took new bids and awarded the contract to the next lowest bidder ($102,900). P sued D for the difference between the two bids. P also sought a recovery of $4,499.60 against D's surety under the terms of the bond posted with his bid. The trial court awarded P the damages it sought. D appealed.