Why That SUV, Jack?

Barbara Birkholz of Fennville, Michigan, writes:

Marilyn: I'm writing about the Jack and Jill clunker puzzle. (September 20, 2009) Why doesn't Jack just trade his SUV for the hybrid? What do not I understand?

Marilyn responds:

The question limits the choices to the two specific trades that the couple can afford. An SUV-to-hybrid trade is too expensive for the couple.