The Question and Answer section for Death of a Salesman is a great resource to ask questions, find answers, and discuss the novel.
Bernard refuses to provide Biff with the answers to the Regent's exam because it is a state exam. To do so could get him arrested.
The meaning of "pay off a house" is quite literal. It means that you are paying off an existing home loan and will no longer owe bank payments. The house is yours.
Do you mean his own state of mind? What act/scene are you referring to?