Betty Buyer Contracted with Dubious to Buy a 2017 Bulgemobile

Betty Buyer contracted with Dubious to buy a 2017 Bulgemobile four-door sedan, colored "avocado green"; Dubious had five such cars on his lot. But on the day Betty was to pick the car up, she telephoned Dubious: Ring, ring; ring, ring: "I'm sorry, but I changed my mind. I'm not going to buy the car." Dubious put down the telephone receiver, and just as he did Dewey Donkers-a customer-approached him, saying, "I'll buy that green four-door there," pointing to the car Betty was going to buy. And Donkers bought the car for the same price Buyer was to have paid.
Ring, ring; ring, ring. "Hello, Dubious? This is Zach Zeller. The good news is we found the Bulgemobile car parts you wanted in Los Angeles. The bad news is we placed the order as you requested, but the parts were destroyed en route to you in a freeway collision while on board Zippo Trucking Company's truck. More later, 'bye for now." Ring, ring; ring ring. "Hello, Dubious? Yeah, Roger here, at Mufflers R Us. I got your request making sure we'd deliver the muffler and exhaust parts by two weeks from Tuesday, as we contracted to do. I don't know-we had problems with our pipe-bending machine for making the exhaust parts up. We might not make the deadline. Just a heads up to you. Goodbye."
Ring, ring; ring, ring. "Hello, Dubious? Carr here. If you haven't sent that 1948 Bulgemobile to Franklin yet, I suggest you don't. He just told me he's gonna have to declare bankruptcy tomorrow. Best regards."
Each of the following questions starts with this phrase: "What remedy, if any, has . . ."
-a) . . . Dubious in the situation with Roger (exhaust pipe bit)?
b) . . . Dubious regarding the '48 Bulgemobile which was, as Carr spoke, en route to Franklin on board a car-carrying truck?