Can you do a step-by-step please, I don't know how they got 504,000, 18000, and 12.5%

Two independent companies, Hager Co. and Shaw Co., are in the home building business. Each owns a tract of land held for development, but each would prefer to build on the other's land. They agree to exchange their land. An appraiser was hired, and from her report and the companies' records, the following information was obtained: The exchange was made, and based on the difference in appraised fair values, Shaw paid $90,000 to Hager. The exchange lacked commercial substance. Hager should recognize a gain on this exchange of a. $0. b. $18,000. c. $90,000. d. $144,000. The best answer choice is: b All Answer Choices - a - b - c - d