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On January 2, Sue contracts to sell and Bertha contracts to buy five cases of racquet balls at $200 per case for delivery on February 1. The balls are to be shipped F.O.B., Bertha's city, and Bertha is to pay after receipt and acceptance. On January 15, Sue informs Bertha that she will not perform. On February 1, Bertha buys balls that are reasonable substitutes for $225 per case. Bertha sues Sue. The measure of damages is (assuming no incidental expenses)