Gains and losses when trading in a vehicle

There are 3 pages after your mileage deduction calc that ask for Sales Price, Vehicle Cost, Gains and loss. 

When vehicle is traded in and has only used mileage deductions, for both  biz vehicle (both 98% biz), is the Sales Price page even used, if so, do you input trade in value shown as sales price? Vehicle Cost page is the sales price of new vehicle minus trade in?

then Gain or loss Basis is again the trade value if car isnt worth much or mileage x a given percentage from the year previous? (as depreciation-even though you never depreciated vehicle) It seems like your getting hit on this 3 x's. I'm confused.

Using 3000 as a trade value- 30,000 as final cost of new vehicle including the trade, how would these numbers input on those pages?

Thanks for the help