Heuristics, Biases and Risk Preference Assessment

An individual is endowed with a limited-edition corporate souvenir mug. The individual's baseline valuation (acquisition value) of the mug is $15. Assume a standard prospect theory value function where utility for gains is v(x) = x and utility for losses is v(x) = -λ|x| for x < 0, with a loss aversion coefficient λ = 2.25. If there is no transaction utility, what is the seller's Willingness to Accept (WTA) to part with the mug compared to a buyer's Willingness to Pay (WTP)?