who do i have to speak to to buy a house in Solitude? please

http://www.uesp.net/wiki/Skyrim:Proudspire_Manor

"To purchase the home, the player must first complete a miscellaneous quest for the Jarl of Solitude. Upon completion she will permit you to purchase the house from Falk Firebeard for 25,000 gold. Ownership of this home is required to become a Thane of Solitude."