Donna runs an inn and charges $300 a night for a room, which equals her cost. Sam, Harry, and Bill are three potential customers willing to pay $500, $325, and $250, respectively. When the government levies a tax on innkeepers of $50 per night of occupancy, Donna raises her price to $350. The deadweight loss of the tax is

a. $25.

b. $50.

c. $100.

d. $150.