1. What is the total sales tax to be paid in 2012 on the purchase of a 2012 passenger vehicle with a selling price of $17,000 and a $2,000 trade-in allowance?

It depends upon the state. Some states to not require the purchaser to pay sales tax on the entire selling price if a similar vehicel is traded in.

For example, see (for Ohio)
http://www.brunercox.com/ohio-sales-tax-trade-in-allowance/

You have not said what the applicable sales tax RATE is in the state where the vehice was sold.