Suppose I do? and Supposing I do? 30508

Suppose I do? and Supposing I do?
Inf. And what does it matter if I do? What are you going to do about it? Alice: Do you really think it's right to do something like that? Sue: Suppose I do? Fred: Are you going to drive up into the mountains as you said you would? Sally: Supposing I do? Fred: I'm just asking.