A and B have a contract. B, in turn, has contacts with C, D, and E, that cannot be fulfilled if A breaches the contract with B. If A breaches the contract knowing of B's contracts with C, D, and E, what is the name of the damages that B can recover from A to compensate B for his loss of the contracts with C, D, and E? Also, what is the name of the principle that holds that B cannot simply sue A for breach, but must first make a reasonable attempt to find someone else to perform as A was supposed to have done?