Consider an English auction for a watch with two bidders, where bids must be raised by at least $1.

The seller believes that the first buyer's valuation is $5 with 1/3 chance, $10 with 1/3 chance and $15 with 1/3 chance,

whereas the seller believes the second buyer's valuation is: $5 with 1/3 chance, $12 with 1/3 chance and $15 with 1/3 chance.

(a) What is the seller's expected revenue with no reserve price?

(b) Can the seller increase her revenue by setting a reserve price of $10, $12, or $15? If so, which of the three reserve prices should she pick to maximize revenue?